Going by the explanation provided here, it sounds like it's dragonball/Z. Which I suppose would be appropriate for OP's profile picture.
It's an odd term to say the least. It's directly under martial arts/ wuxia. Unless there's a more specified meaning, the terms there already define the type of story it is.
Meanwhile, isekai has an actual meaning of "another world", where the character is transported to another one. They can be of any theme, but reincarnation/time travel do not necessarily cover "another world". So isekai as a tag is actually appropriate in tagging a story and not just containment. Lv2 Kara Cheat for example has no reincarnation or time travel, but the MC is just moved from one fantasy world into another.