The following is not hilton specific as I've limited hilton experience but, just to stress what Jenbel posted above:
These should really be viewed as descriptions of the room concept, not the actual bed(s) you will receive.
- A 'single' means you will get a room that is at least capable of sleeping 1 person, and the bed will probably be a single bed. The room you get could be a twin, double, anything, so long as it can sleep 1 person. Obviously the hotels have fewer true single rooms than other types as they are the least flexible.
- A 'twin' means your room should definitely have two *separate* beds. What beds you get could be from 2 single beds upwards. A single and a double, two doubles, three singles, ...
- A 'double' means your room will be capable of sleeping two people who can be expected to share a bed. Generally that explictly means a bed for two people, but you will find the odd hotel which will supply 2 separate beds as you are just saying you are willing to accept a bed for 2 people together.
As I said, the room you get could be anything that meets the requirements you are expressing. In the past I've booked singles and been given every type of room imaginable.
NOTE FURTHER: What a room is
capable of sleeping and what you are paying for can be two separate things.
You will sometimes find if you book a twin you are told (in advance) you are getting 2 double beds, or if you book a single you are being guaranteed a double bed, etc.
That is NOT saying that you would be entitled to sleep X number of people in the room, even if it officially has room for X sleepers. You may find the rate for a room with 2 double beds varies depending on the number of people staying in it.
In conclusion, make sure your booking reflects the number of people you want to stay in the rooms. Additionally, make sure it reflects your requirements - i.e. if you need separate beds make sure it is a twin/triple/quad or make sure that you have a 'guaranteed room type'.