What is an xPub?
An xPub also known as extended key- can be thought of as a 'read only' view into a wallet. An xPub allows full view to all transactions, addresses, and balances in a specific wallet, but doesn't allow spending of any kind.
Why do xPub's exist?
Bitcoin wallets create a new Bitcoin address everytime you click receive in order for the person sending you Bitcoin not being able to check the total amount of Bitcoins you have in your address.
How do I find my xPub key?