fg

Bring last job to foreground

$ fg

$ fg %[1]

$ fg %[vim]

fg [jobspec]

fg resumes a suspended or background job in the foreground. It's a shell builtin used with job control to manage processes started from the shell.
Jobs are typically suspended with Ctrl+Z or started in background with &. fg brings them back to interactive foreground execution. Without arguments, it resumes the most recent job.
fg works with the shell's job table, which tracks child processes for job control.

JOBSPEC

Job identifier: %N, %string, %%, %+, %-.

Job number N.

Job whose command starts with string.

Current job.

Previous job.

Only works in interactive shells with job control. Job numbers change as jobs complete. Background processes may have continued running.

fg is part of POSIX job control introduced in the C shell and later adopted by Bourne shell derivatives. It enables managing multiple processes from a single terminal.

bg(1), jobs(1), kill(1)