Below are some terms you will see on IMDb so I thought I would make sure everyone knows what they mean.

 

Pre-production
The planning stage in a film's production after the project is finally greenlighted, and before principal photography or actual shooting commences, involving script treatment and editing/rewriting, scheduling, set design and construction, casting, budgeting and financial planning, and scouting/selection of locations. No celebrities have arrived yet to begin filming.

Filming/Principal Photography
The main photography of a film and the time period during which it takes place. (Production) Also, refers to the filming of major and significant portions of a film production that involves the main/lead actors/actresses.
Only send to a celebrity during the time of which their film is filming.

Post-Production
the final stage in a film's production after principal photography, involving editing, the addition of sound/visual effects, musical scoring, mixing, dubbing, distribution, etc. In other words, all celebrities have now left the location and is no longer filming.

In Development/In production
The state of a film being developed. The stage at where most planning takes place for a film (locations for filming, budget, cast, etc.) At this stage the film has no yet been green-lighted.