Meaning

noun the state of being flexed (as of a joint)

noun deviation from a straight or normal course

noun act of bending a joint; especially a joint between the bones of a limb so that the angle between them is decreased

originBorrowed from Latin flexiō, from flectō (“to bend, curve”) + -tiō, possibly via French. By surface analysis, flex + -ion.

Etymology from Wiktionary, CC BY-SA 3.0