I've heard the term 'backbeat,' I've heard defitions, but I never understood what people were talking about. However, another thread on this page inspired me to look for backbeat on YouTube. Here's what I found:

see it, hear it

The teacher doesn't say so, but we should notice that the big drum, which is played with the foot, is softer than the snare drum. So when he plays

One   two   three four, he's also playing

soft LOUD soft LOUD

Convention says that music in 4/4 should go

REAL-LOUD soft Pretty-Loud soft

but playing on the backbeat changes that.

Whew! I'm glad I won't go to my grave never having understood the backbeat.