Extreme Newb question... What does "bind" mean?

This post was from a user who has deleted their account.

This post was from a user who has deleted their account.

This post was from a user who has deleted their account.

This post was from a user who has deleted their account.

If you no longer need a Soulbound item, you must sell it to a vendor.

Or disenchant it, if your character is an enchanter.

A couple of other miscellaneous uses of the word "bind" in the game:

bind a key to a slot on an actionbar
bind your hearthstone to an inn somewhere
bind your hands behind your back so you can't play wow again all day long omg jesus