a Dreamsome is a pure fantasy of yours. It includes a threesome or above (foursome, fivesome, sevensome, ect.) of hot people you would do. Pretty much it's something you would LOVE to happen although there is only a 0.0001 chance of it happening. hence the inclusion of the word -Dream.
Since these are not very likely to happen, you will probably think of these fantasies when you are masturbating.
Dude 1: fuck....if those girls were all drunk at a party and i was there.....man.....perfect Dreamsome right there!
Dude 2: haha true true
Dude 3: aaawwwww.......i need to go masturbate now....