Dream pop is a genre of music where timbre and texture are as important, if not more so, than melody and song structure. Vocals when present are subsumed within the music and act as another texture or instrument. For example guitarists in dream pop played with feedback and effects to blur and mutate notes, to produce pure iridescent noise, not memorable melodies and toe-tapping tunes, although these were present, they weren't the focus.
The Cocteau Twins are widely recognized as pioneers of the dream pop sound, their sound is a collage of soft, almost indecipherable vocals and languid soundscapes. A.R. Kane were the first band to explicitly describe their music as 'dream pop' and once claimed that "a lot of the time we're trying to transform dream imagery into sounds." Which echoes My Bloody Valentine (who are a premier Dream Pop group who had a huge influence on 'shoegazers' like Slowdive and Lush) approach to recording music while in a state between sleep and wakefulness (hypnagogic).