What do the numbers mean?

For example, in a 5.1.2 home theatre setup:
The first number “5” describes how many speaker channels are present in your setup — left, right, center and 2 rear speakers.

The second number “.1” describes the addition of a subwoofer for more bass.

The third number “.2” describes the number of upward firing speakers for overhead sound.

Together, they build an immersive surround sound experience right at home.