From WoWWiki

Bind can have three meanings in World of Warcraft:

1. To change an item, so it cannot be traded to another character (or put up for auction at the Auction House); this is also known as Soulbound. Also see, Bind on Pickup and Bind on Equip. There is a warning before you preform an action that binds an item to your player.
2. To set the teleport destination of your Hearthstone, as in bind point, i.e. which Inn your hearthstone will teleport you to.
3. To set a keyboard character as a hotkey.

Item Binding Type

All items are also classified by how they "bind" to a player. Item binding types fall into one of four types:

Bind on Equip (BoE) 

Items of this type are soulbound to the first player to equip the item.

Bind on Pickup (BoP) 

Bind on Pickup items are just that, they bind to a player as soon as they are looted. Players must take great care in instances not to accidentally roll on these items if they do not intend to use it. A warning will appear before you roll or pickup a BoP item.

Bind on Use (BoU) 

Bind when object is first used. This is used for objects that are used but do not need to be equipped, like small pets. A warning will appear before it binds.

No bind 

These items can freely change hands. Examples of this are recipe materials and most consumables such as health and mana potions, health stones, food and water, etc.

Binding to an Inn

interact with innkeeper innkeeper out of range

Talk to an innkeeper at any inn to change your bind point (the place where you will teleport to when you use your hearthstone).