Fleece/fliːs/ Definition 1 of 4Pro Tip 1/2Shearing Time Fleece is often mentioned in the context of shearing sheep, usually once a year. The farm engages in fleece gathering every spring. Pro Tip 2/2Natural Insulation Fleece refers to a natural insulator, providing warmth for sheep and goats. A sheep's fleece keeps it warm during cold months.