A cookie was an old Earth food item usually made of water, flour, sugar, and other ingredients, and baked in an oven. Cookies were sweet, and were served as a snack or for dessert. They were often kept in cookie jars. (ENT: "Breaking the Ice")
Shannon O'Donnel had a ritual of purchasing a bag of chocolate chip cookies whenever she went back on the road to "treat herself". Her eventual husband, Henry Janeway, preferred oatmeal cookies since he was allergic to chocolate. (VOY: "11:59")
"I like this major of yours… she's a tough cookie."
- - Kay Eaton comments on the "character" Major Kira Nerys in Benny Russell's story "Deep Space Nine" (DS9: "Far Beyond the Stars")