shoulder season is a period of time between high and low seasons, where prices at a Destination are between their highest and lowest, and the crowds are thinner
Other definition:
Shoulder Season is the period between high (peak) and low (off-peak) season.
Other definition:
Shoulder Season is the that period when there is lower demand for a particular destination. In Alaska, this is usually the fall/winter seasons.
Other definition:
Shoulder season is the those periods between the peak and off season when destination demand is moderate.