Though a previous poster described it pretty well...
No problem. Let me spell it out in layman's terms.
A "Staple" record: often heard in the original oldies format...a song that has tested well in most situations.
(Think: "Brown Eyed Girl")
A "Tertiary" record: One that may have been a hit when it first came out, but has not fared as well in terms
of recognizability and/or popularity over the years. It may test OK to play. But is not
what is considered a "power" record for the format. (In other words, kind of
recognizable, but not a "Good Vibrations".)
A "Lunar" record: Unless you are a hard-core record collector or oldies geek, you probably couldn't tell
someone the name of the song or artist. (Think: "A Letter To My Teenage Son by
Victor Lundberg" which, I know, peaked at #10.)
There's other radio terms, too...but this will give you some idea of what I'm talking about.