A retardant slows a specified process. The word needs a qualifier, such as fire retardant or vapor retarder, to explain what the product is intended to do.
What this means at your property
A coating described as fire retardant and a layer used to limit vapor movement perform different functions. Neither label should be read as a promise that the material prevents all fire damage or all moisture entry.
What should a specification identify?
Ask for the exact product, intended application, supporting documentation and installation conditions. Confirm how it interacts with the rest of the assembly instead of substituting one broadly described protective product for another.