"Crop" a combination of "crap" and "pop." Also, something that is cultivated and grown for consumption. Crop Punk is any of a number of bands popping up in mainstream media that seem to have the exact same sound as every other band on the radio. Very common circa 2005-2006.
This can also be applied to hip-hop, aptly named hip-crop (crap-hop). Around mid 2007 it seemed that the hip-hop industry was, while keeping a few legitimate artists, cranking out one-hit wonder after one-hit wonder. These artists would be what is called "hip-crop."
A: I just got the new CD from Simple Plan!
B: You listen to that crop punk?
A: *Listening to iPod* "I'm hot cuz I'm fly! You ain't cuz you not!"
B: What are you listening to?