They are focused on defining layout, information architecture, and interaction. Color, typography, photography, copy, texture, and any other elements of visual design are reserved until a later phase of the project. Wireframes take less time to change and can be iterated upon independent from visual design aspects. This decoupling is part of what allows designers to work effectively in the product development process.
Wireframes often begin using low fidelity tools such as whiteboards or sketching with paper and pen. Sometimes they evolve into higher fidelity vector-based outputs with tools such as Sketch or Illustrator. When necessary, Wireframes may be annotated and packaged as a formal deliverable and shared with stakeholders or other departments for feedback or further work.