A croissant was an Earth food originating from France, and was usually consumed at breakfast.
Croissants were available from Burgerland in Detroit, Earth, in the year 2004. (ENT: "Carpenter Street")
A holographic simulation of the Café des Artistes of 2342 had menus that listed a croissant available with cheese sauce and fresh tomatoes. (TNG: "We'll Always Have Paris")
In 2368, Captain Jean-Luc Picard and Doctor Beverly Crusher ate croissants for breakfast while they discussed the empathic metamorph, Kamala. (TNG: "The Perfect Mate")
After Lieutenant Commander Data was sent back in time to the year 1893, a bellboy named Jack brought him a croissant wrapped in the day's newspaper. (TNG: "Time's Arrow")
In 2370, Picard and Crusher agreed on coffee and croissants for breakfast everyday while they were linked together by the psi-wave device on the planet Kesprytt III. (TNG: "Attached")