S1 is the power state to "suspend" the CPU. Power is still used in this state and it can be thought of as a light sleep. Higher numbers represent deeper sleeps such as S4 "hibernation", in which context is saved to disk and no power is used.
There are 6 different modes.
S0
S1
S2
S3
S4
S5
S0- Working
S1-: All processor caches are flushed, and the CPU(s) stop executing instructions. Power to the CPU(s) and RAM is maintained;...
Hibernation. In hibernation, everything in ram is copied to a file on the hard drive and then the system shuts down. Later, when a power button is pressed, the system does not have to go through the...