Shell job.
See What is the Ampersand (&) in the Bash Shell ? ie the Asynchronous, Parallel control operator
If the terminal is destroyed (which can happen if it was a pty, like those created by xterm or ssh, and the controlling program is terminated, by closing the xterm or terminating the SSH connection), the job will fail as soon as it tries to read from standard input or write to standard output.
The notion of current job.
fg set a job as current.