A schedule is a plan of things to be done and the time when they will be done. It is the thing you write down in your planner. If you're a student, you probably have your class schedule memorized within the first few weeks of school.
This noun derives from Middle English sedule "slip of parchment or paper, note," from Late Latin schedula, from scheda "a strip of papyrus," from Greek schida "a splinter of wood." The modern spelling schedule did not become established until the mid 17th century. And the current American pronunciation, patterned on words such as scheme and school, was not in use until the 19th century.