"Lalita"

She is also variously known as Tripura Sundari- she who is beautiful in all 3 worlds of the cosmos, Shodashi- she who is eternally 16 years old, and Rajarajeswari- She who is the King of Kings. She is in essence Parvati, Shiva's wife.  In Tibet she is known as Kurukulle (Goddess of the Heart Beat Clan).
"Kurukulle"

This bindu point also corresponds to a sacred seed syllable associated with God. There are 3 traditional seed syllables placed at this central point: OM, SHREEM, and RAM. OM is the sound of God Absolute bringing into being the creation of the universe, SHREEM is the sound of blessing that the Goddess bestows in her devotees life, and RAM is the supreme sound of joyous devotion in the heart of God.

9 triangles intertwined- These 9 triangles represent the 9 planets of Ayurvedic Astrology. If properly drawn there should be no gaps between triangle, i.e. each upward or downward point of a triangle should touch the horizontal line of the next triangle. Further, there should be 5 triangles pointing downward, which is the feminine, and 4 triangles pointing upward, which is the masculine. The 5 triangles pointing downward are pointing to the East, to the element water, and to the worshipper, for the Sri Yantra should be laid on the ground with the 5 downward triangles flowing to the devotee.  The 4 upward triangles are pointing away from the devotee to the West and the element fire. More on the four directions when we come to the outer square fortress which houses the Sri Yantra.
There is often an error in positioning the Sri Yantra in regards to these 9 triangles. The variation is 4 triangles pointing down and 5 pointing upward. In this case the central triangle becomes an upward pointing triangle. In this inverted arrangement, the bindu point is often missing. Symbolically, this variant arrangement turns Lalita's temple upside down, and drives the Goddess out of her central dwelling point.
This was done by certain teachers who were afraid of the awesome power of the Sri Yantra. In order to protect the user from its allure, the yantra was turned on its head and emptied of its indwelling Goddess.

43 individual triangles- Though the 9 interlacing triangles form more than 43 triangles, there are 43 unique triangles that are traditionally formed from the interaction of the 9 major triangles. They are usually colored, oftentimes red. There are 42 outer triangles each containing a female yogini who worships Lalita, and the central 43rd triangle which contains Lalita herself and her throne.  These 43 triangles, from the outer edge to the center, form the following 5 groupings: 14 triangles, 10 triangles, 10 triangles, 8 triangles and a central triangle. The outermost and lowest triangle at the bottom of the diagram is triangle 1, while the central triangle containing the bindu point is triangle 43. The triangles progress in a counter clockwise spiral ending in the central 43rd triangle. This 43rd  triangle is the throne of Lalita which is a swan shaped scarlet bed supported by the Vedic male Gods of  Brahma, Vishnu, Rudra and Indra. By their close
 association to Lalita, these four male Gods become androgynous.  The plank of the bed itself is a sleeping Shiva which Lalita sits upon. These 43 triangles contain the 51 letters of the  Sanskrit alphabet as 35 consonants and 8 pairs of vowels. Finally, 43 conceals the holy name of Sri Vidya, for Sri is valued at 2 in Sanskrit while Vidya is valued at 41. Together 2+41=43.

An inner ring of 8 lotus petals- These petals should have no gaps between and should touch the outer ring of 16 lotus petals. The 8 petals contain the 8 female Matrikas of the Sun who form all sacred mantras and divide the 51 letters of the Sanskrit alphabet into 8 groupings. These petals unfold in the directional order of West, North, East, South, Southeast,  Southwest, Northwest, Northeast.

A outer ring of 16 lotus petals-  The 16 outer petals contain the 16 female Nityas of the Moon. They represent the 15 waxing phases of the moon (from new to full) and the  moon as a whole. Each petal is a Sanskrit vowel. These 16 also represent the 16 kalas (or secretions) of the yoni of Lalita. 15 are known, while the 16th is secret (and confers spiritual enlightenment). These petals unfold in a counter clockwise spiral starting with the bottom petal at the West.

Three concentric rings or girdles- This bit of symbolism is missed in most executions of the Sri Yantra. They represent 3 cosmic oceans corresponding to the 3 worlds of the Cosmos. The outermost is a ring of milk, the middle a ring of blood, and the inner a ring of ambrosia. These 3 rings correspond to Moon, Sun and Fire. These 3 rings are found in all Tibetan mandalas and are shown as the outer circles at the edge of the diagram. They are often a tri-colored flame, sometimes waves of water, and sometimes clouds.

3 outer square fortresses- These fortresses are often not shown as three. However, the correct symbolism is 3 interlocking square fortresses with gates at the four cardinal directions (more on the gates below). The fortresses are actually 25 in number and sit upon the top of Mount Meru, the mystical mountain at the center of the universe.
Mount Meru is seen as a central mountain surrounded by 3 smaller mountains, one Northwest one Southwest and one East of Mount Meru. The 3 lesser mountains forming a triangle are made of silver, gold and crystal, corresponding to moon, sun and fire. Mount Meru forms the central point of this triangle. Note that these mountains form the original shape of Sri Yantra- a downward pointing triangle with a dot at the center.

"Sri Meru"

Upon Mount Meru are 25 interlocking fortresses each one higher than the last. These are the 25 fortresses which are divided into 3 basic groups, each group being one interlocking fortress in the Sri Yantra diagram.
The outer square is composed of the first 11 fortresses, each a precious metal. The middle square is composed of the next 8 fortresses, each a precious jewel. The inner square is composed of the last 6 fortresses, each a precious substance of the mind. All 25 protect Lalita from the outer world.
At the top of the 25th fortresses is an infinite lake, made up of 3 oceans (which are the 3 rings). Only the purest of heart can cross this lake and get to Lalita's temple. Floating at the center of this 3 ringed lake is an island made of 1000 lotus petals (in 2 concentric rings, the outer being white and inner being red).
And cradled by these lotus petals is the temple of Lalita made of wish fulfilling gems which sparkle as a 43 faceted crystal. At the very top and center is Lalita's throne bed, which shows Lalita as the Queen and Mother of the Cosmos joined to her lover and husband Shiva.
Note that in the Tantric yantras the square fortress is invariably outside the circular ocean.  With Tibetan mandalas, the fortress is always inside the circular ocean.

4 gates at the 4 corners of the fortresses- The triple fortress that surrounds the Sri Yantra has four gates at the cardinal points. They can either be drawn closed or open. In the closed version, the Goddess is seen at center protected by these gates. In the open version, the devotee can enter the fortresses and arrive at last at the center in the presence of the Goddess. These two versions correspond to the two basic visualization approaches to Sri Yantra. To visualize this yantra from the center to the outside is the act of Creation and takes the viewpoint of the Goddess. To visualize this yantra from the outside to the center is an act of Dissolution and takes the viewpoint of the devotee.
These 4 gates correspond to the four directions in space. In turn these 4 gates are each one of 4 elements, and one of 4 colors. These correspondences can be seen in the Medicine Buddha mandala of Vajrayana Buddhism:
The gate below- the direction East, the element water (apas), the color blue (or white).
The gate to the left of the viewer- the direction South, the element earth (prithivi), the color yellow.
The gate above- the direction West, the element fire(tejas), the color red.
The gate to the right of the viewer- the direction North, the element air /wind (vayu), the color green.
In this directional scheme the center (which is the 9 interlocking triangles) is the fifth element of space (akasha). If blue is used for the direction East, then the center is white. If white is used for the direction East, then the center is blue.

In closing, it should be noted that the Sri Yantra is a diagram that is part of the Shaivite tradition (that worships Shiva), since Lalita is the most esoteric manifestation of Shiva's wife, Parvati. As such, the Sri Yantra can lead to the spiritual unfolding that the yoga of the ascetics can bring about.  In this instance, the Sri Yantra reflects the 9 centers in the spiritual body known as the chakras (the lowest charka being the square fortress and the highest charka being the bindu point).
It is also the paramount symbol for the Sakta tradition, that worships Mother as God Absolute, since Lalita is the paramount manifestation of Mother as God. Here the Sri Yantra opens the heart of the devotee completely to the love of God.
Finally the Sri Yantra is also a symbol for the Vaisnava tradition (that worships Vishnu), for as a yantra of Lakshmi, Vishnu's wife, it is the prime symbol to bring good luck to the devotee. As pointed out at the beginning the name Sri is also the name of Vishnu's wife who dwells in a magical locket on his chest. Note also that the outer 10 triangles of the Sri Yantra are traditionally seen as stations for the 10 avatars or manifestations of Vishnu (which includes Rama, Krishna and Buddha).