An étude was a type of musical composition.
In 2367, Geordi La Forge, while trying to select the perfect music for his meeting with Leah Brahms, considered a piano étude by Johannes Brahms, but dismissed the idea as "too corny". (TNG: "Galaxy's Child")
In 2370, Melora Pazlar asked the computer of the USS Orinoco if there were any Vulcan études on file, and, upon hearing that there were, asked the computer to play something by Delvok. (DS9: "Melora")