From Tom’s Guide website:
The biggest difference between Dolby Atmos and traditional surround sound is the use of channels. Audio over conventional surround sound is confined to 5.1 (five speakers, one subwoofer) or 7.1 (seven speakers, one subwoofer) channels.
Dolby Atmos ditches the channels and assigns the sound objects to a place. That means that if a sound occurs in the top right corner of the room, the audio will have spatial accuracy instead of being relegated to the right speaker. And because Atmos-compatible speakers have integrated upward-firing drivers, you have the added benefit of height.