What is "rollmop"

Usage examples of "rollmop".

She started in at breakfast on canned sardines, two hours later, unless there happened to be customers in the shop, she would dig into a case of Bohnsack sprats, for lunch she would demand fried flounder or codfish with mustard sauce, and in the afternoon there she was again with her can opener: eels in jelly, rollmops, baked herring, and if Matzerath refused to fry or boil more fish for supper, she would waste no breath in arguing, but would quietly leave the table and come back from the shop with a chunk of smoked eel.