Referring to Wednesday as "hump day” is a tradition in American English. It refers to the idea that a week — especially a work week — is like a hill. Monday and Tuesdays are days when you climb up, since they are the beginning or start of your work week. At the end of Wednesday, you’ve reached the pinnacle of the week, and your work on Thursday and Friday represents climbing down toward the weekend.

Hump day then refers specifically to that middle of the week point, where you reach the crest of your journey and begin to pace downward toward the end of the week. If you have a tedious job or just work hard, it can be comforting to reach hump day. Then, the weekend doesn’t seem so far off and nebulous as when you started work on Monday.

There is some dispute about whether Wednesday is truly hump day. Especially when the expression emerged, many people worked a six-day week, and had only the Sabbath or Sunday as a day of rest. Some suggest that in this context, Thursday would have actually been hump day. Also, if you are simply looking at the course of the week, Thursday is the fourth day of the week and in the direct middle, if your week begins on Monday. Yet, many people count the beginning of the week as Sunday, and that makes Wednesday the true middle, whether or not you are using “hump day” in reference to working.