25 or 6 to 4 by Chicago. What does it mean?

What does it mean? It means you’re taking Robert Lamm (the songs writer) way yonder too seriously. ;-)

Blood, Sweat, & Tears, and then Chicago (who sprung up in the wake of the success of B,S,&T), were really a Godsend for the guys playing horn in the High School marching band. Historically considered squares/nerds, it was suddenly okay to be a trumpet or trombone player. Saxes were different, always a cool Rock ’n’ Roll/Jump Blues instrument.

The thing about "horn bands" is that, since the horn players are full members of the band, it is apparently felt that they must play on every song, whether or not the song benefits from them doing so. Whereas The Beatles in their later years would occasionally have a song part played by a horn (Penny Lane, Savoy Truffle, etc.) for a musical reason, horn bands have to give the horn players something to play on every song. I don't care for that concept. I felt the same way about the string players in ELO. It's putting the band members before the music itself, rather common in Rock music, imo.