low season 
noun British
The least popular time of year at a resort, hotel, or tourist attraction, when prices are lowest: ferry connections are sporadic in the low season [as modifier]: low-season prices...
- If you're lucky, you might even find low-season prices combined with high-season weather.
- Catch low-season rates at many Montana wilderness lodges up until the river-fishing season starts on the third Saturday in May.
- A reactive low-season policy is not a credible solution, especially in an industry that does its marketing a year or two in advance of the results.