Defining a pin ## question

What pin ## would this declaration correspond to? I came upon this code and don’t understand how the B has anything to do with the definition and the compiler isn’t marking this as an error.

#define PLM_CS B,2

BTW I am using an Arduino UNO board.
Thanks in advance!

Can you provide a source code line where the symbolic constant is used?

(Second Google hit, after this thread)