A dry run is a rehearsal. The term appears to come from American firefighting jargon, where dry denoted a practice where the hoses were not turned on. Â Here is this detailed description of a dry run from the Frederick, Maryland News of 28 May 1901: Not less than fifteen or more than seventeen men to each company. Dry run, standing start, each team to be allowed one trial; cart to carry 250 feet of hose, in 50-foot lengths; distance, 200 yards to hydrant, attach and lay one line of hose 150 feet from hydrant, break coupling and put on pipe,...ready for water. ( source ) The phrase today applies to anything that needs to be rehearsed.
"We realized that the important thing was not the film itself but that which the film provoked." Fernando Solanas