The term heavy metal took its name from a line in Steppenwolf's late 1960s hit "Born to Be Wild," and was defined during the 1970s by bands such as Black Sabbath and Judas Priest. As metal evolved, it split off into various branches and subgenres. One of these subgenres is grindcore, which combines elements of hardcore and heavy metal. Characteristics of grindcore include screaming vocals, randomly changing time signatures and heavy distortion, with songs rarely lasting for more than a minute.
According to the Urban Dictionary, goregrind is a an obscure offshoot of grindcore that is even more extreme than grindcore, taking the music into even darker, more cacophonous directions. Vocals are usually pitch-shifted to a very low register, making lyrics difficult to understand. Lyrics of goregrind songs are, as its name suggests, devoted to graphic descriptions of blood, gore and horrific medical procedures. The song "Covered With Feces as Decoration" by the goregrind band Last Days of Humanity is representative goregrind.
The Urban Dictionary defines deathgrind as "a Brutal mix of death metal and grindcore." Deathgrind utilizes cacophonous sounds, including the high-pitched squeals and grunts of pigs. As a result, deathgrind songs are deliberately chaotic; it may be difficult for the nonfan to detect any discernible melody. Bands identified with the deathgrind genre include Cephalic Carnage, Dying Fetus, Fecal Corpse and Cattle Decapitation.
The key difference between deathgrind and goregrind is the former's use of animal sound effects and other disturbing noises. In addition, deathgrind borrows elements of death metal in terms of its force and speed, while goregrind tends toward a more punk-influenced sound. In both cases, however, lyrics are practically impossible to understand, and it's unlikely that the casual music fan unfamiliar with these genres would be able to note much difference between the two musical styles.