Premask is the pressure-sensitive tape used to transfer a cut graphic from its release liner to the substrate or to protect a given surface. The release liner, also called the carrier, backing or backing paper, is the portion of the pressure-sensitive construction that protects the film’s adhesive before it is applied. Premask is applied to...
http://supply55.com/blog/2013/08/learn-the-ins-and-outs-of-using-premask-in-your-vinyl-applications/