@TheFlash080
Isekai means (literally) another world. Sadly, due to the popularity of some (more or less) modern series (Aka Mushoku Tensei, Death March, Tate no Yuusha, etc) people had come to believe that Isekai series are those were a person or a group of people are send to fantasy world (either by summoning, reincarnation, etc) and obtain powers in there. Most often than not, those worlds somehow work similar to videogames too.
Examples of old Isekais series are, for exapmle, Magic Knight Rayearth, Vision of Escaflowne, Digimon Adventures, and you may even said that Inuyasha too, even if I personally think that is more time travel than isekai.