A kayak is a narrow one- or two-person boat that is propelled with a double-ended paddle. You can use a kayak in the ocean, on a pond or lake, or in a river.
When you get in a kayak and start paddling around, you kayak (the verb). People who visit the beach often rent sea kayaks and kayak around the shore and between small islands. An even more adventurous way to kayak is in a whitewater kayak on a fast-moving river. Kayaks were first built and used by Inuits, Aleuts, and Yup'iks, and the word comes from the Inuit qayaq, "small boat of skins."