Framework
A large body of prewritten code, built in one language, that handles the repetitive parts of an application. React and Django are frameworks.
What it tells you about a developer
Framework depth signals shipping experience in that framework's home territory: React means web interfaces, Django means Python backends. Peer frameworks in the same language are weeks apart for an experienced developer. Treat the language as the durable skill and the framework as the current preference.
Frameworks let developers skip problems that are already solved, and they also dictate how an application is structured. Every framework belongs to a language: React to JavaScript, Django to Python, Rails to Ruby. Framework skill always implies skill in the language underneath it.