carbon paper

Từ điển Việt Anh Việt 4in1 - English Vietnamese 4 in 1 Dictionary

ˈcarbon ˌpaper BrE AmE noun [uncountable and countable]
thin paper with a blue or black substance on one side, that you put between sheets of paper when ↑typing on a typewriter in order to make a copy onto the second sheet of paper