Sub1Ghz is a group of frequency in the range below the 1ghz.
The ISM radio band definition/allocation are here.
The Sub1Ghz frequency are useful for remote control for example for gate opener, long range sensors, home alarm, water and gas metering, etc.
In Sub1Ghz frequencies normally are used a different modulation 2(G)FSK, 4(G)FSK, OOK, ASK, etc, but also are available two particular technologies that are LORA and SigFox.
For some particular applications, like metering, normally is used the Wireless M-Bus protocol.
Remember that the distance that theoretically is possible cover depend of some factors that are:
* Output dbm
* Speed of communication (data rate)
Practical experience shows that with the same dbm, antenna and frequency the distance covered is greater the lower the data rate is.
Pay attention that some radio frequencies may or may not be available depending on the countries in which you operate and that there are limits on dbm and transmission and pause times.
Here there is a comparative from SigFox and Lora.