Violent ultra-fast metal riffage. The first grind band was Napalm Death
Grind is pretty repetitious, and the guttural Exorcist vocals make the lyrics pretty hard to understand if not impossible. Which is good for bands like Cannibal Corpse or Carcass, and other bands that have lots of goey lyrics. But bad for any band with political posturing who want their message to get through (this same problem applies to say Crass and other hardcore punk bands, who had as much influence on grind as metal).
The average grind song has the length of 50 seconds, at least for hardcore grind like the early Napalm Death albums or Anal Cunt, who makes their living playing some of the most annoying music ever.
Grind has had some influence on other styles of music, most famously with John Zorn who saw the promise in the total destruction of all things melodic of grind.
And indeed Napalm Death makes the cross over to arty punkers like myself by being arty and gothic. This is what separates some of grind from say black metal or the other forms of metal nonsense.
However I can not stand grind for long. Grind is terribly dull after only a few minutes of it, the total of Napalm Death's first album "Scum" is enough for me.