The LSO is the London Symphony Orchestra: another of London’s big orchestras, and a different group from the LPO. It plays concert music, makes recordings, and is well known for film scores as well as the concert hall. “Symphony” in the name does not mean it only plays symphonies; it is just the name. People say each letter, L-S-O, or they say the full name. If you are reading a CD cover or a concert poster, check which London orchestra you actually have — the letters are easy to skim past.