Energy is sold and bought – exchanged – in the Nord Pool power market. In the market, the price for energy is determined according to demand and supply. One day ahead, each hour of the day has an energy price. This hourly price is called spot price.
If you make an electricity contract where the kWh price is based on market price, it usually refers to this hourly variable spot price. In practice, your energy price varies hourly. You can track the spot prices and optimize your energy consumption to the hours when the market price is low.