Your credit limit (also known as your "credit line" or "line of credit") is the maximum amount that you can charge on a credit card. In most cases, the credit card issuer determines the limit when you open the account and it’s based on your credit scores, among other things.
If you have a very high credit limit, it generally means that you have good credit and have earned the high limit. If you try to charge over your credit limit then the issuer might decline your transaction. Or, they may approve the transaction but charge you an over-limit fee.