Scrum is a framework for complex product development.
It originates, but is not restricted to IT.
It was first presented to the public at the OOPSLA Business Object Design and Implementation Workshop in 1995 by Jeff Sutherland and Ken Schwaber, and ever since optimized and updated.

Key features of this framework are the 3 roles (Development Team, Product Owner, and Scrum Master), the 6 Scrum events (Sprint, Daily Scrum meeting, Sprint Planning part 1 and 2, Sprint Review, and Sprint Retrospective), and the 3 Scrum Artifacts (Product Backlog, Sprint Backlog, and Potentially Shippable Product Increment).

The framework is simple, but not easy. The rules of Scrum are defined in the Scrum Guide.