the short answer
A microcycle is the smallest repeating block of a training plan, almost always one week. It is a single rotation of your sessions, the unit that repeats before the next one begins. Coaches default to a week for a plain reason: life runs on weeks. Work, sleep and family all reset on a seven-day rhythm, so a weekly cycle is the easiest structure for a client to follow. Inside that week, a well-built microcycle sets the order of the sessions, how recovery is spaced, and how the weekly volume for each muscle is spread across the days.
This article is general training education, not medical advice. If you are new to structured training or returning from injury, build up gradually and consult a qualified professional.