There are many job descriptions on any film project. As a community representative, you're most likely to come into contact with the ones listed below. For a comprehensive list, see the Internet Movie Database Glossary
Casting Director - Responsible for hiring the actors and extras for the film.
Craft Services - On-set snacks and beverages for the cast and crew. Separate from catering, which provides full meals.
Construction Coordinator - Responsible for coordinating construction and details of the set, including furniture, working props, models and miniatures.
Director - Responsible for the overall cinematic vision of the film; orchestrating the performance by the actors; and managing all creative elements of the production.
Director of Photography / Cinematographer (D.P.) - Head of the Camera Department. Responsible for the look of the film; working with Director, Producer, Production Designer, and Visual Effects Supervisor to create visual representation of script; selecting camera, film stock, lenses, lighting style and color scheme; and setting composition of each shot.
Line Producer - See Production Manager for a very similar job description.
Location Manager - Responsible for managing the filming locations; acting as the representative of the Production Company for the filming locations; negotiating with property owners on price and type of activity; and securing necessary permits.
Location Scout - Responsible for finding locations for the film during pre-production; and prepares photographs of possible locations for review by the Director and Production Designer
Producer - Responsible for overseeing all phases of production for financial and managerial control; working with the Production Company throughout the filmmaking process to ensure that production is completed on time and on budget; and providing the Director with the needed production personnel.
Production Assistant (P.A.) - the entry-level position on the crew. PAs handle an assortment of odd jobs and errands in the office and on the set.
Production Designer - The "architect" of the physical appearance of the set. Responsible for planning and overseeing the creation of the sets, scenery, costumes, and other items that appear in front of the camera. The Art Director reports to the Production Designer.
Production Manager / Unit Production Manager (U.P.M) - Head of the Production Office. Responsible for keeping track of the budget; approving schedules and call sheets; and hiring and firing crew.
Property Master - Responsible for the procurement, placement and maintenance of set props, hand props and action props. Props are items that are used by an actor; set dressing are items that appear on camera but are not used by an actor.
Set Decorator - Head of the Set Dressing Department. Responsible for working with the Production Designer on set design and decoration; overseeing the dressing of the set with appropriate items; and managing the acquisition of set items.
Transportation Coordinator - Head of the Transportation Department. Responsible for being liaison between other departments and the Transportation Department; and scheduling and coordinating drivers for actors and crew, to and from set.