What does booking a flight with a Y class really mean, other than being very expensive?

I am forced to use a corporate travel agent for booking, and when I check the class of the flight, I on occasion end up with a Y ticket.

My travel is primarily ERJ’s, so I have experienced there is no difference in cabins.

So what does it mean to be traveling on a Y ticket for Elite and non-Elite travelers ?

Sorry for such a basic questions, but this has been nagging me. Been lurking and posting for a couple months now.

Steve