[HardcoreZ28]

Originally Posted by 79T/A

Good catch! What's 'guide coat?' Primer? First time I've heard this term, and it sounds really important!

There's a whole other thread on guide coat but essentially it's a powder or spray that you put on top of your primer...looks like a misted on coat of black. Then you sand and if you have any low spots you'll still see the black when the surrounding areas are clean.
Not sure if you were asking about primer too....but it's basically a type of paint you use to seal in any previous paints if you use a primer/sealer. It also has much better adhesion than regular paint and is used between your bare substrate and your color to help promote the physical bond between the paint and the car.