User-defined fields that you add to families or projects and then share with other families and projects. They are stored in a file independently of a family file or Revit project; this allows you to access the file from different families or project

Revit is often used for designing buildings and creating 3D models of architectural designs. It allows architects to create detailed building designs, visualize the project in 3D, and produce detailed documentation and construction drawings.
Revit is a contraction of Revise-Instantly.