High speeds are generally where you fly somewhere, layover for a period of time which isn't long enough to be a full legal rest period, and then fly again (Usually really late arrival and a really early departure). I'm not fully up on the new rest regulations, but say that the minimum legal rest under the circumstances is 10 hours. If you only have 7hours off between flights, the company can't count it as a rest period at all.

So say your based in Chicago. You leave for La guardia at 10pm and get there at 12:30a. You stay there for 5 hours and then fly back to Chicago at 5:30am. You have a 5 hour sit at La Guardia, but it's not a legal rest period, so you're technically on duty the entire time from when you show for your trip in Chicago until you get back to Chicago and are off duty.

Some guys like this kind of schedule because they're free during the day and if you live in base, you're around for family stuff. I personally can't handle it and feel like I have the flu after I fly a redeye, so they don't work for me, but to each his own.

There are several terms for this type of flying.........High Speed, Stand up overnight, CDO (Continuous duty overnight), etc They all mean the same thing.