Power is defined as the time rate at which work is done or energy is transferred ($P = W/t$).

1. Derived Unit: Since the SI unit of work is the Joule (J) and the SI unit of time is the second (s), the unit of power is Joule per second ($J s^{-1}$).
2. SI Unit Name: In the International System of Units (SI), this unit ($1 J s^{-1}$) is given the special name watt (W) in honour of James Watt.
3. Conclusion: Since 1 watt is defined exactly as 1 joule per second, both terms represent the unit of power .