Yantra is the Sanskrit word for “instrument” or “machine”. The meaning is contextual. Much like the word ‘instrument’ itself, it can stand for symbols, processes, automata, machinery or anything that has structure and organization. One use popular in the west is as symbols or geometric figures. Traditionally such symbols are used in Eastern mysticism to balance the mind or focus it on spiritual concepts.
Look up the description and benefits in Pyramid Yantra for Vaastu Book on Page 111, 133