Noun
a way of letting you know that someone else is calling when you are using your telephone
Source: WordNetThe Internet is the most important single development in the history of human communication since the invention of call waiting. Dave Barry
I think about the automobile, I think about like, when I was a kid, you know, the invention of the answering machine, which I was like, 'Wow.' Or call waiting, which was, like, very big. It was a very big thing. Call waiting was a very big thing. And these incremental innovations happen constantly. Ashton Kutcher