shoulder season
n. Travel industry term for the time period between a tourist area's peak and low seasons.
Many of them, no longer tied to school schedules, are discovering the "shoulder seasons" in the spring and fall, when almost everything is less crowded, but not yet covered in snow.
—Jerry Adler, “Why Can't We Get Away?,” Newsweek, July 27, 1998
Discounts on accommodations and recreation — such as a seven-day scuba stay at Harbor Village on Bonaire for $ 997 per person — are also cropping up on different islands this early spring, known as the "shoulder" season in the trade.
—Gary Lee, “What's Up Down There,” The Washington Post, March 01, 1998
1970 (earliest)
February is a "shoulder season" month. At least, that is what Lufthansa Airlines calls it. "On season" is when an airline has its peak travel period, and in the case of Europe, this would be roighly April tlmough September. Fares are higher than than in the "off season," which is approximately November through February.

"Shoulder season" is an in-between travel time, and the fares are also in-between. February. March and October would be considered "shoulder season," and quite pleasant months to take a trip to Europe.
—Adalene Ross, “It's a Woman’s World,” The Times (San Mateo, California), January 30, 1970
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