An off-season bodybuilder is a bodybuilder who is focused on adding mass to his body in between competition seasons. Competition season for bodybuilding typically runs from around April to October, so November to March is the off-season.
Off-season is also called mass-building or bulking. Bodybuilders increase their amount of muscle through exercise and diet while working to improve in specific areas as needed. During this time, they are preparing for future competitions and shows by following a specific diet that depends on their size and goals. For example, they commonly eat much more protein, carbohydrates and healthy fats during off-season periods.