A "Yooper" is someone from the U.P. - the Upper Peninsula of Michigan ;-) Here are a few yooper terms as heard by Arika Okrent:
1. HOLY WAH! The Yooper version of "Holy cow," "whoa," or "duuuude" depending on the intonation.
2. PANK To pat something down to make it more compact. You'll want to pank down the snow real good if you aim to make a sturdy snow fort.
3. BIG MAC The Mackinac Bridge. The one that connects the U.P. to the "mitten" that makes up the rest of Michigan, and that brings all the tourists up in the summer.
4. SISU Many of the settlers of the U.P. came from Finland, and some useful Finnish vocabulary has made its way into the dialect. Sisu is a Finnish word for grim, hardy perseverance. To make it through a winter up there, you've got to have sisu.
5. TOIVO AND EINO A pair of Finnish names that refer to the lovable, hapless characters that are the basis for a whole genre of Yooper jokes, such as: Toivo and Eino decide to head down to Motor City. After they cross the bridge they see a sign that says DETROIT LEFT. So they turn around and go home.
6. CHUKE A basic knit winter hat. Comes from the French-Canadian word toque.
7. CHOPPERS Deer skin mittens with a wool insert.
8. SWAMPERS Rubber boots to be worn in muddy terrain. Go well with choppers and a chuke.
9. TROLL Someone from the lower part of Michigan. Cause they live under the bridge, doncha know.
Historical perspective: In early 2014 Merriam-Webster announced that it was putting "Yooper" in the dictionary. The Upper Peninsula of Michigan is connected to the rest of the state by only one little four-lane bridge (actually the longest suspension bridge in the western hemisphere), and in its relative isolation, has developed its own distinct culture.