A catch-all term for popular music from the 1920's-early 1960's - jazz vocalists, big bands, barbershop, lounge singers, etc. So named because most of the remaining living fans of this music are quite elderly and can sometimes be seen at casino concerts with their scooters and oxygen tanks. In the radio business, the format is known as "adult standards" and is sometimes lumped into terms like "easy listening" and "beautiful music".
You went to see Bobby Vinton at the county fair?! I can't believe any of his fans are still alive; that had to be an oxygen tank music crowd. I bet you were the youngest person there.