Say your writing a program using vi, and you want to check your email. You do not have to open a new terminal. Job control will let you go back to your shell and run a new program without leaving the program your on.
Job control refers to the ability to selectively stop (suspend) the execution of processes and continue (resume) their execution at a later point.
More information can be found using man bash.
The most common way to suspend a program is CTRL+Z. This is the key the shell looks for while running a program. Some programs override that key however. For example, to suspend bash itself, use the suspend command.
When you suspend a program, you will be returned to the shell, and the shell will give a number, identifying the job.
+ Stopped vi jobs.html
The number in square brackets is the job number. On the right is the program that was suspended.
Type jobs. You will see a listing like this:
 Stopped su (wd: /etc) + Stopped vi jobs.html - Stopped telnet
There are two ways to start a job.