means The stretch of time when a sport isn't being played competitively — the gap between one season ending and the next beginning.

from A plain English compound of 'off' (meaning inactive or away from duty, as in 'off duty') and 'season' (a recurring period, from Latin 'satio,' a sowing or planting time, via Old French). 'Season' first meant the agricultural sowing window, then broadened to any cyclical stretch; 'offseason' simply marks the part of that cycle when the main activity is switched off — a usage that grew with organized sport and tourism, where business or play runs hot and then goes quiet.