A sandwich is a meal in the form of two pieces of bread with meat, cheese, or some other filling between them. Your favorite lunch might be a peanut butter and jelly sandwich.
When you put something between slices of bread, it's a sandwich. It's named for the Fourth Earl of Sandwich who's credited with inventing it. Sandwich is a verb too, that describes putting something between two other things, like sandwiching gym class between math and lunch. Sometimes sandwich involves being squeezed uncomfortably, like having to sandwich yourself between people on a crowded elevator or subway car.