A transactional revenue model is one in which the customer has to make a purchase every time to obtain the product or service. For example - shoe stores, toothpaste companies, hiring a mover, etc.
A subscription revenue model is one in which a customer must pay a recurring price at regular intervals for access to the product or service. They make one transaction that will last a period of time. For example - meal kits, newspaper subscriptions, gym memberships, etc.