I'm using Digital Signal Processing Principles, Algorithm and Applications 4th Edition written by Proakis and Manolakis. In Chapter 3, subtopic 3.3.2 it mentions the term "causal signal" which I can't find any definition. I know what a causal system means: a system that output depend entirely on past and present input, not future input but here it's causal signal, not system
So what does causal signal definition?
I tried to look at the Index and it says that the term "Causal Signal" is mentioned in page 85 but in fact, I find nothing in page 85 mentioning it