When driving a manual transmission car, what does 'riding the clutch' mean, and why is it bad practice?

1. Keeping your foot resting on the clutch pedal while driving; it causes premature clutch plate wear, slippage, and overheating
2. Using the clutch to change gears smoothly
3. Pressing the clutch fully down when coming to a complete stop
4. Releasing the clutch smoothly when starting from a standstill