A proposal is an offer. When making a marriage proposal, get down on one knee. When making a business proposal, try to stay off the floor.
A proposal is a suggested plan or offer. After overhearing the marriage proposal, everyone in the restaurant watched in silence, waiting to hear your answer. At least you said "yes" to dessert. There are other types of proposals besides marriage offers: "Your proposal that the dollar be replaced by a new currency made of cheese has gained support from the dairy industry."