Sweater is what hockey people call the jersey. Not “jersey,” not “shirt,” always sweater. If you say “jersey” around a locker room, people will still know what you mean, but you’ll sound like you just started watching last week.
The name is actually older than the sport’s modern uniforms. Early hockey players really did wear thick knitted wool sweaters on the ice, back before anyone had invented a lighter, game-specific fabric. The gear changed decades ago. The word never did.
In a sentence: “Grab your sweater, warmups start in five.”
Also worth knowing: a team’s home sweater is usually the dark-colored one, and the away sweater is usually white or light-colored, the opposite of how a lot of other sports do it.