Just as it says.
If you want to stay in a Hilton over a weekend between now and 31st January.
Looks like it's not just UK hotels either.
You can either go online (see link) or phone 0870 607 1144 and quote P78EXO
Updated - Apologies to those having trouble. You will need to enter the code into the very bottom of any of Hilton's search pages. As mentioned lower down the thread, it is for weekend stays only so it's either Fri.Sat.Sun or Sat.Sun or Sun only.
There are at least three codes that seem to do something similar P78EXO, P82EXO and PR09SW.
For it's worth, I'm in a Queen Suite with Exec lounge access in Paddington for the same price as the Travelodge...
It looks like HUKD takes the launch page away so try http://www.hilton.co.uk/exclusive6
rather than the link.