Terminology
The etymology of gratin is from the French language in which the word gratter meaning "to scrape" or "to grate" as of the "scrapings" of bread or cheese, and gratiné, from the transitive verb form of the word for crust or skin. The technique predates the current name which did not appear in English until 1846 (OED, s.v. "gratin").
In addition to the well-known potato dishes such as Gratin dauphinois, cooking Au gratin is a widely used cooking technique in the preparation of numerous dishes including many meat, fish, vegetable and pasta dishes, fennel, leeks, crab meat, celeriac and aubergines (eggplant).
The term le gratin signifies the "upper crust" of Parisian society, and, as gratin, has since been borrowed into English.
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