The word "preliminary" is a valid word in the English language and is widely used. You can use the word when referring to something that has been done as a preparation for something more important. Example sentence: The research team has completed the preliminary stage of the project.

The easiest way to define preliminaries in construction is as a group of items necessary for a construction company or contractor to complete a project but that won’t become a part of the finished work—site overhead, scaffolding, powering the site, etc.