What do you call the depressed areas in a gun barrel that help impart spin to a bullet?

The correct term for the depressed areas in a gun barrel that help impart spin to a bullet is "grooves." In the context of rifled gun barrels, the design includes ridges and grooves that create a helical pattern. The grooves are the recessed surfaces that, along with the lands (the raised portions), create the characteristic spiral movement of the bullet as it exits the barrel. This spin stabilizes the bullet in flight, improving accuracy and range.

Understanding this terminology is essential for comprehending how firearms operate and the importance of barrel design in ballistics. Familiarity with the mechanics of grooves and lands will also aid in forensic analysis, as the unique patterns left on a bullet can help link it to a specific firearm.