Most people use the job number to refer to a job, because one number is easy to remember. However, jobs can be referred to in a number of other ways: by process id, current/previous job, or all or part of a job name. If we had these jobs:
$ jobs —l  + 466 Stopped split —5000 hugefile  — 465 Running find / —name —print &  463 Running sleep 25 &
then the split job could be referred to as %3, %+, %%, 466, %split, or %?sp, the find job could be referred to as %2, %–, 465, %find, or %?f, and the sleep could be referred to as %1, 463, %sleep, or %?sl.
|%+, %%||current job|
|%string||job whose name begins with string|
|%?string||job that matches part or all of string|