Cornichons are pickled gherkin cucumbers. In France, these tart pickles are classically served with pâtés and smoked meats. In other countries, they are apparently served with small, fried strips of fish.
Gherkin (French cornichon) is a young cucumber (Cucumis sativus), picked when 1 to 3 inches (3 to 8 cm) in length and pickled in jars or cans with vinegar (often flavoured with herbs, particularly dill; hence, ‘dill pickle’) or brine.