Combed, mercerized, and gassed cotton

Dear users and authors,
you often come across the phrase “combed, mercerized, and gassed cotton.” What does it mean?

As far as I know, the term “gassing” dates back to earlier times when stray hairs on wool were singed off using gas burners. Today, there are more modern methods for this. Mercerization is a chemical process that cotton undergoes to achieve a lustrous finish. Cotton is, by nature, a rather dull yarn.