This is a real treat, children, even if JTW and I are the only ones who really groove on it: some very rare footage of the original, vintage Chicago (then still Chicago Transit Authority, I believe) performing their signature number 25 or 6 to 4.
What does the title mean? Despite theories and speculations, it is simply a song about writing a song. Bobby Lamm looks up at the time. It's about 3:35 or 3:34am... or, to put it another way...
(We say our Josiah was born at "35 or 6 to 4.") (UPDATE: DAOD points out that beloved grandson Timothe was born 37 or 6 to 4... but pm, in this case, not am.)
That gave you a great peek at the late, great guitarist Terry Kath — most underappreciated guitarist, ever — in all his awesomeness. As is the following, which features both Kath's picking and his awesome, one-of-a-kind jackhammer strum: