Human: I'd like to know what the difference is between a scuba diver and a free diver. Assistant: 
A scuba diver uses a self-contained underwater breathing apparatus (SCUBA) to breathe underwater, while a free diver does not use SCUBA but instead relies on natural buoyancy and swimming ability to stay afloat. Free divers are often called "sport divers" because they dive for fun rather than as part of a professional diving job.