kW and kWh
kilowatt · kilowatt-hour · power · energy · 킬로와트
A kW (kilowatt) is a unit of power: how hard electricity is made or used at a moment. A kWh (kilowatt-hour) is a unit of energy: how much is made or used over time.
kW measures power, the size of the flow at an instant. kWh measures energy, power multiplied by time. Using the same kW for longer means more kWh.
Korea's market rules state generator capacity in MW, bid available capacity in MWh, and prices such as SMP in KRW/kWh. KEPCO bills use both units too: the basic charge is based on contract demand (kW), while the energy charge and fuel cost adjustment charge are applied to energy used (kWh).
News-reading tip: watch for articles that mix up 'capacity' (kW) and 'generation' (kWh). A large installed capacity does not mean a large actual output. The concept linking the two is the capacity factor.