Difference between Transmigration and Isekai

People tend to consider transmigration and Isekai to be the same which is just wrong,

Transmigration is the soul or the consciousness of a person travelling to another world inside an already existing person who had memories and past and all that, example: "The greatest estate developer" and "LOTM" and even "Overlord" (not sure about Overlord though)

Isekai is a very broad term which can be further divided into 3 aspects, rebirth, reincarnated and summon, all of these are to a different world and are mostly after death or just a summon, example: Re:Zero, Konosuba, TBATE, Tensura and Mushoku Tensei