Chicago was formed in the late sixties in (where else) Chicago and released their first album in 1969 - the self-titled Chicago Transit Authority. The group changed their name shortly after the album's release when the actual Chicago Transit Authority threatened legal action.
That first album, which featured hits such as "Does Anybody Know What Time it is?", "Questions 67 and 68" and "Beginnings" soared up the charts, going double platinum and making Chicago a huge success just two years after their inception.
A year later the group produced their second self-titled album (as all their albums essentially are), Chicago, or as it is sometimes called Chicago II. On this album was the song "25 or 6 to 4." This song features a catchy bass riff at the open and strong horn parts. Not really rock, but much more than jazz, the beat really keeps you moving when you run.
The strange title is actually a reference to the time of day: 3:35 (or 3:34) - 25 (or 6) to 4 AM. You may need to read that a couple times before you get it - I had to. This meaning becomes a little more clear when you think of the opening lyrics: "Waiting for the break of day..."
The lyrics are weird, talking about sitting on the floor trying to stay awake while "waiting for the break of day." Like many (most?) songs of the 60s and 70s there were rumors that the lyrics were drug related - I can certainly understand that, if not, then what exactly do they mean?