Order 37 was one of a series of contingency orders that the clone troopers of the Grand Army of the Republic learned when they were being trained on Kamino. It dealt with using a large amount of civilian hostages to force the capture of an individual. It involved suppressing local civilian populations, including mass civilian arrests and civic lockdowns, and then issuing an ultimatum: if the local populace does not turn over said individual, all the arrestees will be executed. Though it was rare troops ever had to use this order as it was a last resort to capture the wanted individual(s)
A follow-up file for Order 37 was entitled: Scenarios for Body Disposal Post Order Thirty-Seven.