So I have SRAM Rival groupo and they say it has trim, but I am not quite sure what that means. From what I have gathered it is a way of adjusting your derailleur on the fly so that the chain stops rubbing, is this correct?

correct.

I have heard many say that SRAM doesn't really have trim, but I am pretty sure I used it yesterday.

Yup, that's what trim is. I'm not sure how SRAM does it, but there's 1 or more extra clicks for the front shifter so you can nudge the front derailleur a bit when you're cross-chained or almost cross-chained. If things are set up well, though, you may never need to use the feature. My Campy Chorus group has trim also, and I basically never use it.

I definitely have to readjust my front derailleur. I dropped my chain three times yesterday. The trim seems to be right before one would shift down in the left shifter. I didn't quite realize that was what it was. I tried to shift and I heard the click, but nothing seemed to happen. I tried the same thing later (I don't know why) when I had cross chain and it went silent. Any way, after yesterdays ride I have a few adjustments I have discovered that need to be made.

I switched to new pedals before the ride (SPD to LOOK) and didn't even think about adjusting saddle. I was regretting that about 10-15 miles into the ride. I guess that small difference in cleat thickness and pedal thickness can make a huge difference in comfort.

Yet another reason to carry a multi-tool.

And I did. I guess I forgot to mention that I adjusted it.

I thought this thread was about something else.

I like trim....