Well, for example: Look at that cubby belly!
Meaning: A belly pertaining to a cub.
Or: That is a hot looking cubby!
Meaning: An attractive chubby/bearish guy, usually of young age and none to moderate body fur.
For me a cubby is basically someone younger than me, chubby, some fur (although not necessarily), cute/baby face… There are two ways to go about defining a cub. You can go by looks (like I just described) or you can go by role. As in a Bear and his cub, in which case the cub is usually the younger, submissive partner. I tend to use a mixture of the two.