Where does the term "shoulder season" come from?

[Rookie1]

I dont care what it means, I have never said it and will never call it shoulder season. Ill stick with fall and spring.

 

[johnnylabguy]

"Shoulder," in addition to the body part, also refers to a sloped area usually abutting something else -- for example, the chimney below has a double shoulder:

That chimney looks cold. It should put a shawl on it's shoulders and light a fire of soft maple and poplar.

 

[cat-face timber]

You guys just do not get it..
What shoulder season means is, when you can carry your nights wood in your arms.

Or when we take our yearly bath and we need somebody to dry our shoulders.