The grace period is the maximum amount of money you can charge on the credit card time before the credit card company starts charging late fees least amount of money that must be paid at the end of a month period of time before the credit card company starts charging interest

period of time before the credit card company starts charging interest

Explanation:

The grace period is the period of time before the credit card company starts charging interest.

Let's say the  billing cycle on your credit card goes from the 17th of May to the 17 of June.  Starting May 18, you enter a new cycle... and you can charge any amount of purchases (respecting your limit of course) and not pay a single cent in interest if you pay your bill in full and on time on the 17 of June.  That's the smart way to use a credit card... to extent the period you have to pay your purchases.