Wireframes are a basic visual guide used in digital design to suggest the layout of fundamental elements in the interface. Because of this, they are often completed before final visual designs are developed. When completed correctly, they provide a visual reference upon which to structure each screen.

Wireframes also act as a way to communicate with clients and stakeholders. Over the course of a project, the process of wireframing provides a stable foundation on which to consider alternate user paths or new requirements. The information architect and information designer often use wireframes as working documents on which to establish the language, content, and structure of interactions users will have with a given product.

— Adapted from Wikipedia, Website Wireframe