non-reactive pan

I've heard 2 different definitions

doesn't react to acidity

doesn't react to heat

so which is it chefs?

To me, non reactive pans/bowls are nonreactive to acidity. I.e. don't make sushi rice in a metal bowl that isn't non-reactive :D
Unless you like your rice to taste like metal, of course.

Depends on whether or not you soak some bread crust in cream to make your hamburgers

non-reactive to acid. don't make lemonade in a metal garbage can.