A macro is an application that automatically clicks for you, there are different modes and you can set delays inbetween clicks. I use OP Autoclicker to spam doors in minecraft and to spray the Tec-9 fast in CS:GO. I'll put a screenshot of it here.
A chat related macro is when you bind a button via a different type of program (Razor and Logitech has these) and you make it open the chatbox, type something, and send it, I used to have it but Windows 10 uninstalled the Logitech application for some reason and I haven't gotten around to reinstalling it, hoped this helped!