People often think of filmmaking as the everything that happens from production onward, but getting ready for that first day of filming is incredibly important and a lot of work. This phase of prepping for the shoot is pre-production which usually referred to by the shorthand prep.
Pre-production is the first, very practical step in the filmmaking process. Whereas development is somewhat amorphous with every film or TV show having a different story of its development process, pre-production is straight-forward in approach if not execution. This is not to say it is easy, nor that different projects deal with different problems, but the basic work that needs to be done can be clearly broken down with allowances for each project's unique characteristics.
The steps in pre-production have a rough order of execution, though they may shift a bit and certainly overlap. As in production and post, there are departments, each dealing primarily with one aspect of prep. Below will be a breakdown of the steps in pre-production by department in their rough order of start (very little is 'finished' in pre-production and nearly every aspect continues on at least into the beginning of production).