A promisor is someone who makes a promise to a promisee.
Promisor is important in contract law because we are usually asking whether the promisor is legally obligated to keep his promise.
For example, if A promises to pay B $500 then A is the promisor and B is the promisee. Contract law will tell us whether or not a court will make A liable if he does not keep his promise. Consider the following, A promises to pay B $500 and B says, “Great! Now I can get that tablet computer I always wanted.” Is A in legal trouble if he decides not to pay? That’s the answer you can figure out by studying contract law.
Often, you will see more than one promise being made in a case. A person can be both a promisor and a promisee if he has exchanged promises with the other party. So be careful, and don’t lose track of who is the promisor and who is the promisee with respect to each promise.