Coil stamp

This 2-cent coil stamp of the US 1954 Liberty series was used heavily throughout the 1950s and 60s.
A coil strip of British 1957 Scouting commemorative stamps with the trimming of the perforations on one side clearly visible.
A vertical coil pair with a joint line, US 1917.

A coil stamp is a type of postage stamp sold in strips one stamp wide. The name derives from the usual handling of long strips, which is to coil them into rolls, in a manner reminiscent of adhesive tape rolls. A large percentage of modern stamps are sold in coil form, because they are more amenable to mechanized handling in large quantities than either sheet stamps or booklet stamps.