There is a billing cycle for a credit card which is usually monthly in nature.
The spends for a month are taken together and then a bill is generated for the total amount spent less any payments made.
The month is not always a calendar month in terms of dates but it depends on the policies of a bank.
The customers billing cycle could be from the 2nd of one month to the 1st of the next month or it could be from 16th of one month to the 15th of the next month or even 24th of one month to the 23rd of the next month.
This period remains constant and every month the bill would be generated for these specific dates.