Music video games are games which have you holding plastic things that kind of resemble real instruments, if real instruments were made of plastic, weighed 2 pounds each, and were color-coordinated to keep your drunk ass from fucking up too much.
In 1997, Konami, a company most known for Metal Gear Solid, Castlevania, and a shitload of crappy NES games, created Beatmania, a video game simulating a DJ turntable. The next year, they created Dance Dance Revolution, a game you might have heard of, because between controversies about games letting you shoot children in the face the news still needs stories about video games and made a big deal about this one leading to (*gasp!*) exercise. As a result of the 15 minutes of fame, Konami was able to capitalize on their success by releasing such entries as Dance Dance Revolution Disney Mix, Dance Dance Revolution Mario Mix, Dance Dance Revolution Strawberry Shortcake, and My First Dance Dance Revolution, which I understand also allows you to shoot children in the face.
Then in 1998, they totally ripped off Harmonix' Guitar Hero by creating Guitar Freaks, a game that had you playing with a plastic guitar controller, holding down colored "fret" buttons, and strumming in time with the music.
In 2003, Harmonix created Karaoke Revolution for Konami, marking the first time that a Konami music game had songs that people actually wanted to interact with or had heard of before the video game. As a result, Konami let Harmonix get away from them and develop music games for Activision, a company much worse off than Konami, that Konami thought needed a hit a little bit more.
In 2005, Harmonix created Guitar Hero, published by Activision, which had people using plastic guitars to simulate playing real guitars, which led to many real guitar players to complain about how unrealistic the gameplay was and many people who never played a real guitar not to care and play the plastic one anyway. Again, unlike Konami's Bemani music games, Guitar Hero had songs that people had actually heard of and liked. Imagine that. Followups included Guitar Hero 2, Guitar Hero 3, Guitar Hero 5(but never a Guitar Hero 4), Guitar Hero Rocks the 80s, Guitar Hero Aerosmith, Guitar Hero Van Halen, Guitar Hero Metallica, Guitar Hero Stevie Wonder, Guitar Hero Elton John, Guitar Hero Mario Mix, and a Guitar Hero where you shoot children in the face.
Somewhere in the middle of all that, Harmonix left Activision to be bought out by MTV Games to develop for EA, two companies that were in danger of going under and needed a hit badly. Since Activision still owned the rights to Guitar Hero, they needed an original idea to compete.
As a result, they created Rock Band, a game that has you playing a plastic guitar synchronized to licensed music. Oh, and you could sing. And it was just like Karaoke Revolution. And you could play Bass. Except that was stupid, because bass players suck. Except Sting. And Lemmy. And drums. Which worked just like the guitar except even easier because you didn't have to time colors AND strums, JUST colors!
Activision responded by handing over the reigns of Guitar Hero to Neversoft, a studio that had just finished running their once-loved Tony Hawk's Pro Skater series of games into the ground. They handled the license by countering Rock Band with Guitar Hero 3, a game that played exactly like the first two and introduced nothing new to the table.
Harmonix countered with Downloadable Content(German for "stuff we could have put in the game but held back to charge you more for". Those Germans have a word for everything!) out the ass. Literally out the ass. By the end of 2009, they had more than 5 songs available for download. If you wanted songs that they didn't put on the original disc, you were in luck, especially if you like songs by Boston bands nobody's ever heard of. They even made it so that these songs would be playable in future games, such as Rock Band 2, Rock Band 3, Rock Band 4(The Undiscovered Country), Lego Rock Band, and Rock Band: Shoot Children In The Face.
Neversoft responded to this volley with Guitar Hero World Tour, a game which plays exactly like Rock Band, except the drums have one more pad.
Harmonix responded with more Downloadable Content, to which Neversoft responded by adding 1 song of DLC to their game.
Activision has branched out their music franchise by introducing DJ Hero, a game that isn't at all like that Beatmania game mentioned earlier, what are you talking about, here smell this rag and tell me if it smells like chloroform. They've also launched Band Hero, a game that is completely new and isn't at all like Guitar Hero, despite being the exact same thing.
Konami has responded with Rock Revolution, their way of apologizing for creating the genre by trying to destroy it with absolutely shitty gameplay. Absolutely shitty. Just awful. An XBOX 360 Achievement earned by playing Rock Revolution is the music video game equivalent of a Purple Heart.
Konami has also relaunched their Karaoke Revolution line of games, now with actual master versions of the songs instead of licensed covers, 3 years after Harmonix started exclusively using masters in all of their songs on Rock Band, which plays like Karaoke Revolution, plus has Guitar Hero in there too. Good job there, Konami. Never too late, huh?