Yantras are diagrams for meditation.
They have evolved over time through consciousness-explorers, sadhus, tantriks, rishis.
The yantra Symbolising Blessings From Maa ChinnaMasta presened above. The yantra consists of a triangle with a bindu sitting inside three circles, and the three circles sit inside a reverse triangle, which is enclosed within a circle, and the circle sits atop a lotus with eight petals. The Lotus is enclosed with a square shaped enclosure, with four sides PROTECTED.