Are these two styles interchangeable? I looked them up and both have their own separate wikipedia article, and each one is defined as being a fusion of death metal and grindcore. Is this true? I don't know anything about them so I was just curious if anyone knew the difference between them if any.

I'm not entirely sure on this, but I'm pretty sure that deathgrind is simply death metal mixed with grindcore, while goregrind is basically a stripped-down version of deathgrind with a few distinct elements added (extremely deep gurgles - pitch-shifted or otherwise - for vocals, less emphasis on blasts and more emphasis on slow and churning passages and chunky grooves, and overall a darker and more grotesque sound).

Deathgrind: http://www.youtube.com/watch?v=cPml4EKDDdk
Goregrind: http://www.youtube.com/watch?v=nMUl7eWJG9M

a lot of goregrind is heavily influenced by early Carcass, see early exhumed, impaled, and general surgery for examples. Aborted also started off as goregrind. I know this may seem obvious but to some it may not be, but the lyrical themes of goregrind are all gore related. early cattle decapitation is another example.

I find death grind to be more a mixing of death metal and grindcore without the gore aspects of things. bands i consider to be deathgrind would be early willowtip records bands like fate of icarus and commit suicide, which if yo uhave not heard are well worth checking out.

nothing set in stone these are just my opinions/ observations.

Don't forget that a staple feature of deathgrind is the alternating high/low vocals. Impaled play deathgrind, unlike what the previous post stated (unless he meant early impaled, which i havent heard before). Goregrind is closer to grindcore rather than death metal (short, blasting songs) with the main difference being the gore lyrics and vocal style. Pretty much just listen to demo/first album era Carcass and then compare that to their next two.

Deathgrind is like the inbetween point of death metal and grindcore. Longer songs and more parts as opposed to the short songs of earlier grindcore. Look at Phobia's Return to Desolation and anything by Assuck. Assuck has a lot of death metal influence to their grindcore.

Most of the basic have been covered, so I'll just add that in addition to goregrind is obscenely distorted and heavily downtuned. Also I would add that the all mid-paced slower stuff is usually known as "groovy goregrind," which is like another smaller subset of it. though. Most of the original bands were pretty blast heavy - see Last Days, Dead Infection, Jig-Ai, etc.. there's also the semirelated pornogrind & cybergrind

Blasting goregrind: https://www.youtube.com/watch?v=z2Tk7E5zS5s
Groovy goregrind: https://www.youtube.com/watch?v=G09LPLHVEJM
Somewhere in between the two: https://www.youtube.com/watch?v=ec505vEpySA

Death is more of basic mix between death metal and grindcore. I think the new Murder Construct is a pretty textbook deathgrind record, listen to samples of that and compare it to everything else posted and I think you can hear the difference pretty well.

Edit: I did in fact have the same link twice.

You linked TDEBN twice, dude.

Anyways, I personally hear a difference between what you call "groovy goregrind" and the slower stuff I was referring to earlier, and I'd even go so far as to just go ahead and group bands like Cliteater and TDEBN into pornogrind.

The key difference is that death grind just mixes the chaos and punk aspects of grindcore with the sound and song structure of death metal, whereas goregrind utilizes both (as well as heavy early Carcass influence) to sound as disgusting and offensive as possible.

Goregrind is much simpler music, similar to Grindcore but more downtuned, chaotic and messy; with the pitch-shifted or "gurgled" vocals and gorey lyrical matter as its most recognizable feature. The elements it takes from Death metal are more the "brutality" of the music, vocals and lyrical matter than the actual riffs (there's little to no melody in goregrind). It doesn't feel as punk/hardcore and political as grindcore, creating a more grotesque atmosphere similar to that of death metal. The most obvious example is Carcass' debut album Reek of Putrefaction:
http://www.youtube.com/watch?v=kMfjv86YI_A
Other good exponents are Dead Infection, Regurgitate and Lymphatic Phlegm.

Deathgrind has more actual musical influences from Death Metal; it does have Death Metal riffs with more discernable melody, but played with some Grindcore influences on the speed, intensity, vocals, etc... a good example would be Carcass' sophomore record Symphonies of Sickness (compare to the other one):
http://www.youtube.com/watch?v=6YVW9GmPiaM
Many deathgrind bands started playing goregrind; like the aftermentioned Carcass and also Cattle Decapitation, Machetazo, among others.

I have a harder time separating Deathgrind from Brutal Death Metal. Or classifying the incredibly noisy bands like Mortician, Last Days of Humanity (Putrefaction in Progress), Enmity and the mexican Disgorge. (sometimes I refer to those as "Brutal Goregrind")

Deathgrind and brutal death metal are actually quite separate. Brutal death metal is a lot heavier, doesn't necessarily focus on speed, and usually features lower, more obscene vocals. A lot of brutal death metal bands also feature little to no grindcore influence at all (seriously, listen to Disgorge - the American one - and tell me if you hear any grind influence whatsoever).

Mortician are brutal death metal mixed with grindcore, Putrefaction in Progress is a gorenoise album (goregrind + noise), Enmity are just straight brutal death metal, and Disgorge are BDM mixed with goregrind.

To me pornogrind is sort of like "viking metal" in which it refers more to lyrical content and presentation than sound, for the most part. Pornogrind is just really overtly and ridiculously over the top like Gut.

As for BDM and deathgrind... here's what a typical BDM track sounds like: https://www.youtube.com/watch?v=hd0fL3BdSi4
Technical, lots of palm-muted riffs, gurgling vocals, longer songs.

Deathgrind: https://www.youtube.com/watch?v=IP_rQ4ktigQ
More overtly blasty, much shorter, riffs are much less obtuse & slightly punkier

Like MalignantThrone said, there really aren't that many bands that actually mix BDM and grind. The best example I can think of is Inhume, or maybe Circle of Death Children?

Pornogrind usually refers to bands like Gut, CBT, Rompeprop, and Satan's Revenge on Mankind - it's like goregrind with nearly all of its ties to metal completely cut. The beats are a lot more based on rock music (you've got the infamous polka beat that pornogrind bands like to abuse), and the stuff the guitars play is a lot more like chunky chugging than anything resembling a riff.

Roadside Burial do this (albeit not very well): http://www.youtube.com/watch?v=Gf1Cn6Ay7j8

The short version:
Deathgrind is death metal with grindcore influences, while goregrind is grindcore with death metal influences.

Holy shit.

Eh, disagree. Are we hearing the same bands? Gut, CBT and Rompeprop all sound pretty metal to me, they've each got plenty of riffs along with the groove (which is not mutually exclusive with metal). The polka and skank beats are more from the basic punk side than anything else (see Rot). You might be more on the mark about Satan's Revenge though, frankly I'm not too familiar with them. Cybergrind and gorenoise stuff is where it really completely departs from metal, imo. Regardless, it's just nitpicky at this point, I think the thread's been answered pretty completely.