Jalapeño - A small, hot chile pepper, usually green.
Recipe: Jalapeño Pepper Recipes

Jam - A thick, cooked mixture of fruit, sugar, and sometimes, added pectin.
Recipe: Gingered Rhubarb Jam

Jambalaya - A versatile Creole dish, Jambalaya is a combination of cooked rice and a variety of other ingredients. It may include tomatoes, onion, green pepper, meat, poultry, and/or shellfish.
Recipe: Shrimp Jambalaya

Jell - To congeal, often with the addition of gelatin.

Jelly - A clear, cooked mixture of fruit juice, sugar, and sometimes, added pectin.

Jelly Roll - A cake made with a layer of sponge cake spread with jelly or jam then rolled up. Jelly rolls may also be filled with whipped cream or frosting. The cut slices have a pinwheel design.
Recipe: Jelly Roll With Jam or Jelly Filling

Jicama - A brown-skinned root vegetable with a crunchy white flesh and mildly sweet flavor, jicama is good both raw and cooked. Also referred to as the Mexican potato.
Recipe: Snapper with Chiles

Jigger - A liquid measure equal to 1 1/2 fluid ounces.

Johnnycake or Johnny Cake - A flat cake made from cornmeal, salt, and boiling water or cold milk, usually fried like a griddlecake. Today's johnnycakes often include eggs, oil, and baking powder. Some versions are baked in the oven like cornbread. Johnnycake is also called hoe cake or hoecake.
Recipe: Sharon's Johnny Cake

Julienne - To cut food into thin, matchstick strips. Julienne strips are usually about 1/8-inch thick, but the length varies.

Jumble - An old-fashioned, rich sugar cookie.
Recipe: Molasses Jumbles