Structured period of time where learning is intended to occur
A lesson or class is a structured period of time where learning is intended to occur. It involves one or more students (also called pupils or learners in some circumstances) being taught by a teacher or instructor. Generally, a lesson is defined as "a piece of instruction; a reading or exercise to be studied by a pupil; or a division of a course of instruction.
https://en.wikipedia.org/wiki/Lesson