A credit card charge off is when a credit card company agrees to wipe your credit card balance clean so that you owe nothing. Sometimes this can be negotiated if you pay a certain percentage of the balance.
It is when a bank claims your account as "bad debt" on their books after no payments have been received for 6-12 months. They close your account and report it to the credit bureaus. This is bad for your credit but not the end of the world. You will still owe the money to the bank.
When a credit card company declares your debt as a loss for the company it is written off their books as a charge off. It can negavitely affect your credit.