Ya I read what -k is, but no idea what Diablo is. Don't even know if kernel is software or hardware... firmware?
It is a chunk of software that's built as an OpenCL kernel that runs on your video cards. There are many different kernels: phatk, poclbm, diablo, diakgcn, for example. The diablo kernel was written by DiabloD3 for his DiabloMiner, but is also used by CGMiner. Confused yet? Good. 
