Me wrote in :
Hi, a quick one. I read with interest the post about facing a frame a
few days ago. What exactly is facing a frame? I know what chasing the
threads in a bb but can someone give me a simple definition?

Facing is shaving the outer edges of the bottom bracket to make them
perfectly parallel before you install the bearing cups. Same goes for the
head tube before you install the headset. This kind of work is less
important now than in the past.