Snorkeling means floating or swimming near the surface with a mask and a snorkel tube so you breathe surface air while looking underwater. Gear is simple (mask, snorkel, usually fins), little or no formal training is required if you can swim, and depth is typically limited to brief dips of a few meters.
Scuba diving uses a self-contained underwater breathing apparatus—compressed air in a tank with a regulator—so you can stay fully submerged, go much deeper, and explore longer. It needs more equipment (tank, regulator, buoyancy control device, gauges) and formal training/certification for safe recreational diving.
PADI’s comparison frames the core split as air supply: surface tube versus tank-fed breathing, which drives differences in depth, gear, and preparation.
Source: Snorkeling vs. Scuba Diving: Similarities and Differences — PADI