A caper was a small pickled bud of a Mediterranean Earth plant of the same name.
Potato casserole was a favorite dish of Miles O'Brien that contained capers. O'Brien's wife, Keiko, disliked the "little dark things" (capers) it contained. (TNG: "The Wounded")
Capers were used in a sauce – along with mustard, shallots and onions – served with shrimp remoulade at Sisko's Creole Kitchen when Jake and Benjamin Sisko visited in 2372. (DS9: "Paradise Lost")