An egghead song is a song of who's lyrics have content that nobody really cares about, such as with songs like "I Gotta Feeling" and "Boom Boom Pow" by the Black Eyed Peas. Those two songs are like "wtf? who the crap cares about that you "gotta feeling"? No one. That's right. No one."
Egghead songs are questioned to why they exist, and why they are common amongst today's modern music, because people are going like "wtf" to so many different songs that it's not even funny anymore (haha). It's like, they're just trying to make you annoyed by their lyrical content.
In modern culture[]
The term is used often to describe songs, as said earlier, with no meaningful lyrical content, but some people misinterpret the "egghead song" term and think of it as a song actually having a head shaped like an egg (or something). That doesn't make any sense at all.
And it never will.