It may happen that you have send a real big job to the printer, and then you realize that, you forgot to change the paper size from A4 to letter, or any other scenario where you may need to change something in a document already sent to the printer queue, so now you need to cancel it. So first lets see the spooler (Printer queue)
This will list all your jobs sent to the printer.
BJC-250 is ready Rank Owner Job File(s) Total Size 1st ggarron 248 (stdin) 0 bytes 2nd ggarron 249 (stdin) 0 bytes
Now if you want to stop jobs, you can use the cancel command.
You can cancel only jobs owned by you, or by an specified user (provided that you have the rights to do it).
cancel -u user
This will cancel all jobs belonging to a certain user, but, if you want to cancel all jobs, no matter who owns them use this command.