Rye Grass?

I've found a place to go check out some hay and the site says they do 'mixed grass bales' and 'rye grass bales'.
Apologies if I sound dim, but is Rye grass hay actually hay or more of a readigrass type thing?

Obviously I don't want to go getting a bale that will be far too rich for them but I thought I'd ask which is better.

Hay is basically dried grass. There are lots of different type of grasses of which rye is one. It is a common grass used in both lawn and grazing mixes. Your average meadow hay has a lot of different types of grass is it but some mixes have more specific types such as timothy and rye, both of which should be quite coarse.