Define Old Firm Meaning

Old Firm
Two Glaswegian teams, Rangers and Celtic. The only two teams who will ever stand a chance of winning the SPL, Rangers due to their superior excellence, and Celtic due to the fact they always have a 12th man on the pitch - the referee.

During an old firm match at gypsy world celtic were unable to win, so called on the ref to allow a fly kick, and awarded an offside goal and also gave a penalty!
By Pooh
Old Firm
Ingenious Scottish fuckwit identification scheme, whereby knuckle-dragging denizens of whichever godawful weegie hinterland are encouraged to wear either green- or blue- and white leisure gear, with optional cigarrette burns, homemade tattoos, and/or adidas baseball caps, thereby allowing the rest of us to avoid them.

"You can always tell when the Old Firm has been in town, the bins have been ravaged for food, and every shop doorway has been shat in"
"Yes, but their shellsuits add such a nice splash of colour"
By Tamara
Old Firm Bird
When girls pretend to support rangers/Celtic on old firm day in hope of they boy the fancy will show them some sort of attention, usually noticeable by a Snapchat story saying fuck the pope or queen

She’s such an old firm bird
By Tallie