Non-reactive means a pan or bowl made of non-porous material the does not alter or add a flavor to or change the color of a food being prepared.

Typically, you would think of glass, stainless steel, enamel, and glazed ceramics. Stainless steel spoon, or maybe a very clean wooden one.

You would want to use them for foods where a reaction with cast-iron or aluminum would affect the taste or composition of certain acidic ingrediants (e.g., tomatoes, citrus fruits)