I kinda understand it as:
Transmigration - transported to another world (doesn't entail being reborn). I'd personally put possession as a kind of transfiguration. And it sorta crosses into Reincarnation if they're possessing a baby I guess?
Reincarnation - born again into another life
Regression - going back in time
Transmigration and reincarnation is actually the same thing but if we're talking about the plots about it then they can be pretty different (it's not too different if you look at it closely). Transmigration in this kind of things, well it's mostly like getting transported in another/alternate world and like it's either you're in your original body or not. Reincarnation for me is, that one person is reborn again and you're not in another person's body or possessing a different body other than yours. Regression is going back in a certain point of time/time travelling to a certain time or moment in the past just once or over and over again (like YJH).
I'm not good with words (I can't find the right words) so I apologize if this made you even more confused. I tried my best explaining it based on my understandings and how it's actually portrayed in manga/manhwa etc...
I've always read Transmigration in the context of body possession, like a modern person possesses a novel character and the difference to reincarnation is that said characters Past has nothing to do with the new soul in the body/ they are a completely different person after they entered the body
Reincarnation is the same person even if they remember their past life
Regression is jumping back to a point in their life with their memories
With this life of fun has become so complicated lol -
1- transmigration - is when a person who transport to another world without being born but entering world with your orginal form.
2- reincarnation - Born into a body of someone else or enter a body of someone else, who probably be character of the world a person has entered.
3- regression/age regression - concept also come up differently -
•- regression going back in your time it usually happens when a person whose current life become mess due to his regrets of mistakes so he gets once again a chance to correct them.
•- age regression - a person who is old become young again in the current time.
The way I understood it was:
Transfiguration = changed bodies, whether in their same world or a new world.
Reincarnation = died and came back as yourself or a new person, in your world or another world.
Regression = idk lol
transmitigation - isekaid, went to another world
Reincarnation - rebirth
Regression - idk but probably its going back through time
In your opinion, what's the difference between these three words: transmigration, reincarnation, and regression? I've been reading so many comments in webstoons and manga with this kind of plot, but most of the time, they used the word reincarnation when I think the MC is a regressor or maybe transmigration. I'm just curious: how do you guys define and differentiate these three words?