React and Angular, have something in common, but they do NOT have same functionalities.
To answer your question:
There are no general definition for the first one and everything always depends on context. You can read many papers, questions and different opinions on the Internet about that topic. I would short-define a framework as "set of libraries and patterns".
React itself without a context is a modern DOM library with VirtualDOM algorithms behind the scene. It can be a V in MVC. However, React evolved into huge component-based infrastructure and is used altogether with Redux and other libraries. In that case when we are observing application from the architecture level, we can say that React (with all other dependencies) is a "framework".
Angular is a full-featured MVC framework and React can be used as a view layer. Angular has many build-in components like ajax while in React you have to use other library for that: jQuery, fetch, old XHR, whatever else.