[...]
       wait [-fn] [id ...]
              Wait for each specified child process and return its termination status.   Each  id
              may  be  a process ID or a job specification; if a job spec is given, all processes
              in that job's pipeline are waited for.  If id is not given,  all  currently  active
              child processes are waited for, and the return status is zero.  If the -n option is
              supplied, wait waits for any job to terminate and returns its exit status.  If  the
              -f  option is supplied, and job control is enabled, wait forces id to terminate be-
              fore returning its status, instead of returning when  it  changes  status.   If  id
              specifies  a non-existent process or job, the return status is 127.  Otherwise, the
              return status is the exit status of the last process or job waited for.
[...]

wait: wait [-fn] [id ...]
    Wait for job completion and return exit status.

    Waits for each process identified by an ID, which may be a process ID or a
    job specification, and reports its termination status.  If ID is not
    given, waits for all currently active child processes, and the return
    status is zero.  If ID is a job specification, waits for all processes
    in that job's pipeline.

    If the -n option is supplied, waits for the next job to terminate and
    returns its exit status.

    If the -f option is supplied, and job control is enabled, waits for the
    specified ID to terminate, instead of waiting for it to change status.

    Exit Status:
    Returns the status of the last ID; fails if ID is invalid or an invalid
    option is given.