In most *nix applications you can pause the application using Ctrl-Z. To resume the application use the fg command. Typing fg alone will resume the first job that was paused. If type fg [#jobnumber] you resume the job with the specified number. The job number is the sequence number, starting from 1, of the jobs that are paused in the order they were paused.

For example, start editing a text document with vi, then press Ctrl-Z. Now, you are sent back to the shell, as you would if you quit vi (or typed the :sh command), however vi is still running in the background. To get back to vi type fg.

Sources: Vim tips: Working with external commands
Linux and UNIX fg command help