Aptmunich is correct, it's the process priority. The way it works is this:
In user space, nice 20 is the lowest priority, nice 10 is the default and nice 0 is the highest priority a normal user can set their process (to change the nice value, you need to check `man nice` at a terminal). The root user (or any administrator user via the `sudo` command) can also access special nice values of -1 to -20, which get progressively higher and higher in priority until they pretty much use up all the CPU time.
IIRC, the reason it's called `nice` and the back-to-front scale is a silly developer pun. If a process has a nice value of 20, it means that it is a very nice process and will give up its processor cycles to others. If it has a nice value of 0, then it's not very nice at all and will hog the processor if it can