A Bitcoin wallet contains the Bitcoin addresses for which you have the private key (in other words, your own addresses).

Each wallet service differs slightly, with some having several addresses for incoming transfers, and others which create new addresses for Bitcoin change. As such, a wallet typically handles multiple addresses.

It should be noted that the concept of a Bitcoin wallet is not included in the Bitcoin protocol. The simplest manifestation is ultimately the Bitcoin address; a wallet is used to conveniently manage addresses.

Some companies refer to their company's Bitcoin accounts as "wallets," so the definition is vague.