The Goregrind Genre
Goregrind. The genre everyone knows by name, but no one can properly define. 'It's just grindcore with gory lyrics' they say, never mind that gory lyrics were present in grindcore, and proto-grindcore, well before goregrind was even a thing. 'It's grindcore with death metal riffs'. Close, but not quite, as that would more closely fit the description of deathgrind.
To understand goregrind, one must understand where grindcore came from. Grindcore was born out of the desire to make speed/thrash metal more extreme, and to do so the grindcore bands had to go back in time to the bands that influenced the speed/thrash metal pioneers. Speed/thrash metal can best be understood as a fusion between NWOBHM and punk, so it's no surprise that grindcore bands took NWOBHM riffs and punk song structures and made them both 'more extreme' - usually faster and played more aggressively.
But what about goregrind, in that case? The name 'goregrind' implies a parenthood with grindcore, but that is the first mistake. Goregrind doesn't come from grindcore. In fact, the best way to tell goregrind and grindcore apart is that goregrind has no punk influences.
Goregrind is what would have happened if grindcore evolved not from a fusion between heavy metal and punk, but out of a fusion between heavy metal and funk music, or occasionally old-school rock 'n' roll. That is the main difference, and the reason why goregrind sounds so different from grindcore. Rhythmically, melodically, harmonically, even in song arrangement the rules are different, because goregrind is an entirely different genre from grindcore.
To get a good example of goregrind listen to Warkvlt's Bestial War Metal, or anything out of Sewer's discography (minus NecroPedoSadoMaso, which is closer to blackened grindcore). Notice the rhythmic differences between the two genres, as goregrind attempts to expand a theme with harmonically and tonally diverse, but rhythmically related, motifs.