Patches of rubber for repairing inner tubes. They are available in three varieties: regular, feather edged and self adhesive. All are available in a variety of sizes.
These are simply cut or stamped from a sheet of material. The side to be glued is usually slightly sticky, and protected by a plastic film which should be removed just before use. As they are the same thickness all over there will be a sudden change in stiffness of the repaired inner tube at the edge of the patch. This can cause the patch to start peeling from the inner tube if not well stuck.
These are as thick as regular patches in the middle, but get thinner towards the edge. This makes it less likely that the patch will peel from the inner tube if not well stuck. They usually have a metal foil protecting the side to be glued, and a plastic film to support the thin edges while the patch is placed and pressed down.
These are patches of either of the above types, but do not need a separate glue. Simply roughen the tube, peel the protective film from the patch and stick.