A Wadcutter or full Wadcutter bullet. These bullet types are very common with revolver cartridges like .38 special. They have a soup can shape so when they're fired at paper targets, they make perfect circle holes in targets. That can be important in a competition setting where they need to measure your groupings. The one in your picture looks more like an inverted wadcutter bullet, usually those wadcutter bullets have a hollow base, but in the past people made cheap hollow points by loading these wadcutter bullets backwards with the hollow base facing the front. To kind of act like a pseudo hollow point projectile. Which would cause more damage to soft tissue. Do they work in practice? I'm not sure.