pg_dump : Mysterious"-b" switch

Hello,

I notice in pgAdminIII when I get it to perform a backup it uses
pg_dump (of course).  I also notice that one of the switches/arguments
is "-b".  When I looked up the PG documentation
(http://www.postgresql.org/docs/8.1/interactive/app-pgdump.html) I
can't see any reference to "-b".

Can anyone explain what it does?

Many thanks,
-Damian