What does IPX waterproof rating mean?

IPX4: splash proof (light rain, light sweat). IPX5: jet proof (heavy rain, intense workouts). IPX6: powerful jet proof. IPX7: submersible to 1 meter for 30 minutes. IPX8: submersible beyond 1 meter (depth varies). For gym use, IPX4 minimum. For running in rain, IPX5. For swimming, IPX7 8. Note: waterproof ratings don't cover saltwater or chlorine.