In economic terms, electricity (both power and energy) is a commodity capable of being bought, sold and traded. An electricity market is a system for effecting purchases, through bids to buy; sales, through offers to sell; and short-term trades, generally in the form of financial or obligation swaps. Bids and offers use supply and demand principles to set the price. Long-term trades are contracts similar to power purchase agreements and generally considered private bi-lateral transactions between counterparties. Wholesale transactions (bids and offers) in electricity are typically cleared and settled by the market operator or a special-purpose independent entity charged exclusively with that function. Market operators do not clear trades but often require knowledge of the trade in order to maintain generation and load balance. The commodities within an electric market generally consist of two types: Power and Energy. Power is the metered net electrical output of a generator at any given time and is measured in Megawatts (MW). Energy is electricity that flows through a metered point for a given time and is measured in Megawatt Hours (MWh).

Markets for power related commodities are net generation output for a number of intervals usually in increments of 5, 15 and 60 minutes. Markets for energy related commodities required by, managed by (and paid for by) market operators to ensure reliability, are considered Ancillary Services and include such names as spinning reserve, non-spinning reserve, operating reserves, responsive reserve, regulation up regulation down, and installed capacity. In addition, for most major operators, there are markets for transmission congestion and electricity derivatives, such as electricity futures and options, which are actively traded. These markets developed as a result of the restructuring of electric power systems around the world. This process has often gone on in parallel with the restructuring of natural gas markets.