"Credit Terms" are the number of days the customer has to pay the invoice. The days start counting from the invoice date.
It is also possible to start counting from the end of the month. For example, if the invoice date is 15 June, you can specify that the payment is due on the last day of June or the Nth day of the next month (e.g. 5 July).
With this, almost any payment term can be created.