We generally run jobs in bash in serial order. There is another way to run jobs which is named parallel. Running parallel means multiple jobs run at the same time.
$ ping google.com & ping poftut.com &
We can see from the output that after command is issued we have two line which show the commands processes and their related PID and there is also information about the background jobs in square brackets job id. Both command will start in background and will resume up to kill operation or exit.