Actually, "payment terms" in English refers to the set of conditions agreed upon, such as the rate of interest, the time schedule for repayments (weekly, monthly, etc.), the term (total length of the loan repayment period), entitlement to prepayment, penalties for default, etc. "Payment term" (singular) usually refers to the time frame for repayment, such as a 5-year term for a car loan, or a 25-year mortgage on a house. "Term" and "terminate" carry similar meanings of completion dates.
So, prazo de pagamento = payment term (having to do with time, frequency)
termos de pagamento = payment terms (all the applicable conditions)