A rental agreement secures a tenancy for a short period of time, typically a month. Landlords can increase rent, change the terms, or terminate the agreement on short notice. A lease secures a tenancy for a longer period of time, typically a year. During that time, the landlord is not allowed to raise the rent, change the terms or terminate the lease on short notice.
The information for this answer was found on our Month-to-Month Rental Agreement answers.