A non-disclosure agreement is a legal document preventing a designer (or client) from sharing confidential information about a project with third parties — commonly used when a project involves sensitive business information, an unlaunched product, or a name change not yet public.
Most standard branding projects don't strictly require an NDA, since the end result (a public-facing logo and identity) is meant to be seen. It becomes more relevant when early concepts, business strategy, or product details discussed during the project need to stay confidential before launch.
Reputable designers are generally comfortable signing a reasonable NDA when a client requests one — hesitation here is worth asking about directly.