A calque is a word-for-word translation from one language to another. When you take a phrase in French, for example, and translate each word literally into English, that's a calque.
There are many examples in English of common phrases that are calques, translated from other languages. An "Adam's apple," for example, is a calque of the French pomme d'Adam, and "beer garden" is a calque of the German Biergarten. In both cases, the English phrases came from a direct, literal translation of the original. Another term for this is a "loan translation." In French, calque means "copy," from calquer, "to trace by rubbing."