Twink - A skinny gay guy with little to no body hair.
Bear - A gay guy who has considerably more bulk and body hair than a twink. Not necessarily fat or muscle, though could be a combination of the two. Do not necessarily have to have body hair.
Bears have different terms for members within the group:
Bear
Cub - A person who has the qualities of a bear, but usually do not look as mature as a bear does. Usually between 20's and 30's.
Musclebear/Bull - A bear who's physically defining feature is their muscle mass; may or may not have body hair.
Otter - In essence, an Otter is a twink who has body hair.
Manatee - A person who has the traits of a bear, but does not identify as one.
Panda (Bear) - A bear of Asian Descent
Koala (Bear) - An Australian Bear
Ursula - A lesbian bear
Black Bear - Exactly what it says on the tin.
Pocket Bear - A short bear.
Teddy (Bear) - A bear who's face, torso, arms, legs, and back are covered in hair.
Wolf - Leaner than a Bear, but bulkier than an Otter. Often times the dominant one in a partnership/relationship.
Goldilocks - A straight girl who hangs out with bears.
Daddy - A mature guy who goes after younger guys.
Grizzly - A type of bear who has massive height, weight, or amount of body hair.
Chaser - A Non-bear who is attracted to bears.
Chub - A bear who more known for his rotundness, due to considerable weight.
Polar Bear - A bear who has mostly white/gray hair.