A cake is a firework that is constructed from many cardboard tubes glued together. Each tube normally contains a single shot, and these are all connected by an internal fuse. Once the cake is lit, the fuse burns from tube to tube, igniting each shot in turn. Thus, a 16 shot cake will have 16 tubes, a 49 shot cake will have 49 tubes and so on.
Cakes are designed to be set up on the ground. They remain on the ground but each shot is blown out of the tube and into the air above.
Cakes can contain an almost infinite variety of effects and timings. Some cakes are quiet, some are noisy. Some have effects that start as soon as they leave the tubes, others blow a shell high into the air where it bursts into life.