What does it mean when a purchase is pending with Wels Fargo? Also, what's overdraft protection?

It means that you purchased something and the merchant has yet to submit the request for payment. It's in the computer, WF is just waiting for confirmation from the merchant.

Overdraft protection is where the bank covers any check or debit transaction instead of bouncing the check back to the merchant or denying the debit transaction because you don't have the money in your cash account. Many years ago, checks were sent back to the merchant if you were short of funds. But banks got creative and saw a source of money they were passing up. Instead of bouncing the check and not getting any money from you, they would pay the check and charge you with the $39 NSF fee or transfer money from your OD protection account to your checking account (for a lower fee + interest).

It means it has in the process but not completed. Overdraft protects you from overdraft fees (an overdraft is when you take out more money from your account then what is in the account.