It's a term used to refer to applications that run some of the same code client-side and server-side. See: http://isomorphic.net/

In React / Javascript land, isomorphism means, "the same code is used to render on the server and in the browser"

I really really hope the JavaScript redefinition of this word dies out. Please just make a new word instead of butchering a perfectly well-defined one.

It's using the completely correct biology usage: "a similarity of form or structure between organisms"

Thinking it only refers to one field and is wrong - when the usage is totally correct (and very applicable) just makes you sound snobbish... and foolish.

I don't disagree, I come from a maths background so it's a bit weird too; however, I'm yet to see a decent alternative and it's rather entrenched now. It's not a good descriptor however: using the word with non-tech product owners makes their eyes glaze over, so I'd love something better but am yet to come across it.