Shakti is the name given to the creative female principle which is symbolized as inverted triangle which also represents the Yoni; this inverted triangle represents the female energy known as Shakti and in Tantric meditation as kundalini.
What is Shakti ?
As kundalini is known as Serpent power coiled three and a half times at the bottom of the spinal column. The purpose of the yogic Tantric meditation is to arouse it to make it rise up through different chakras until it joins Shiva, the male principle located at the top most chakra known as Sahasrara. When meditation is successful a mystical event occurs in the devotee of Shakti suddenly this dark inverted triangle starts to descend upon the Third Eye, this is the symbol of Shakti.
When kundalini is awakened it sounds angry and it hisses like a serpent. The sibilant hiss continues until it reaches Sahasrara chakra and a mystical event takes place in the union of Shakti with Shiva. Self realization is attained. Shakti represents the kinetic aspect of the ultimate principle; the power that permeates all creation, it also means consort of Shiva.