What mean of Gassed yarn?

Gassed yarn is yarn or thread, which has been quickly passed through a flame or series of flames. The purpose of which, is to burn off the fibers projecting out of the yarn/thread, this will make the yarn/thread round and smooth.

This is most often done with the better qualities of yarn/thread, such as poplin; venetian; violes; gaberdine; and Egyptian cotton; for example.