Roulette

Rouletting is a series of small cuts to allow stamps to be separated from a sheet or pane or from each other. If you've seen a sewing/quilting/dressmaker's pounce wheel or tracing wheel tool, the resulting pattern would be pretty much the same.

In early times where imperf issues were still common, pounce wheels have been used privately or unofficially for separating them. For example, the United States' Kansas City roulette was used at that post poffice in late 1914 to more easily sell an accumulation of imperf stamps.

Otherwise, rouletted stamps were normally created by sharp pieces of metal with the pattern to cut through whole sheets at one go on standard printing presses of the time, just like tickets were and are produced.

That uniform rouletting are measured just like perforations, treating the uncut sections between cuts like perforations. 



Compare with the hyphen hole perf, where actual holes are cut into the paper. However, they can be hard to tell apart on individual stamps.