What is the shoulder season in electricity markets?

Electricity consumption in the U.S. Lower 48 states is highly seasonal; the demand for electricity peaks in the summer and the winter in response to more extreme temperatures and decreases in the spring and fall, in the so-called shoulder seasons, when weather is generally milder. Electric utilities and owners of power-generating assets perform maintenance on power plants during shoulder seasons because of less electricity demand that means that the system generally doesn’t need to be operating at full capacity.