Wireframes are the rough draft of how a website or app will look. They show page layouts, information hierarchy, and user flow. Wireframes can be either low-fidelity, mid-fidelity, or high-fidelity. 

Low-fidelity wireframes are the simplest form. They are often sketched on paper or whiteboards and are used to bring initial ideas to life.

Mid-fidelity wireframes add additional details such as scale, content size, buttons, and menus. This can be done on paper or in a design application of your choice.

High-fidelity wireframes are the most detailed of all. They are a prototype that closely resembles the final design of a project. Imagery, color, font preferences, and line spacing are key details.