Rock music, most likely one of the hardest concepts in music to define. When rock was first born, it was from the merger of blues and country. Rock was defined by its energy and its rebellion of standard. Since then, rock has grown, from humble begins to a fully blown lifestyle. The style of music has changed as well, from Chuck Berry's pounding to the soft groove of Billy Joel, to the heavy, hard hitting AC/DC.
Today, rock has spun of into many variations, yet most hold true to the fundamentals of what is rock music, and that is a number of things. Fristly, like blues, rock is played from the heart; it is played, not made using computers. Second, and I think Aerosmith said it best, "If it is worth doing, it is worth overdoing".
Catagorize it as you like, Rock and Roll, Heavy Metal/Hard Rock, Alternative Rock, Pop-Rock, Punk+New Wave, Soft-Rock, and (late 90's) Grunge.
There is so much excellent rock music out there, ranging from very soft to seriously heavy, only a fraction gets to be played on the radio. The definition of "Rock Music" varies according to who you ask, but it is described in the Ultimate Encyclopedia of Rock as:
Invariably sung and played by the composers themselves - and serious musical themes often called for the length of a full album, rather than a three-minute single, to impart their message. Witness Led Zep, the Flloyd, doyens of the prog rock concept album etc etc.
Strangely, that publication describes it in the past tense, as if it's talking about history. But rock music isn't dead, it just doesn't get much radio coverage. I don't believe most DJs know it even exists. The only way to hear this music is to buy it, or see it performed live - but how do you even know it exists, let alone decide whether you like it or not?
Just succumb to it, let it wash over you & enjoy!