A bilateral contract is one where both sides of the contract agree to do something in exchange for the other side performing a different action. Almost any contract can be considered a bilateral contract as one side agrees to loan money or do something like a job or even offering a job in exchange for something from the other party ranging from receiving the money, taking the job, or whatever is agreed to.
When a bilateral contract is signed, both parties are obligated to provide the service that is written and agreed on. If one party keeps their side of the contract but the other party does not, they can sue to reclaim any loss.