What is a "3 needle BO"?

[LilT23]

I'm just finishing up this vest and have gotten stuck...can anyone please help me?

Here's the pattern: http://knitty.com/ISSUEspring04/PATTboogie.html

Under the part, "Join Shoulders," it says: ...work a 3 needle BO to join these sts...

How exactly do I do this?

Thanks for your help! :D

[Julie]

Go to this page:

http://www.knittinghelp.com/knitting...s/bind-off.php

It's the last video at the bottom.