A pickled cucumber – commonly known as a pickle in the United States and Canada and a gherkin in Britain, Ireland, South Africa, Australia, and New Zealand – is a usually small or miniature cucumber that has been pickled in a brine, vinegar, or other solution and left to ferment. The fermentation process is executed either by immersing the cucumbers in an acidic solution or through souring by lacto-fermentation. Pickled cucumbers are often part of mixed pickles.

The cucumber is a widely-cultivated creeping vine plant in the family Cucurbitaceae that bears cylindrical to spherical fruits, which are used as culinary vegetables. Considered an annual plant, there are three main types of cucumber—slicing, pickling, and seedless—within which several cultivars have been created. The cucumber originates in Asia extending from India, Nepal, Bangladesh, China, and Northern Thailand, but now grows on most continents, and many different types of cucumber are grown commercially and traded on the global market. In North America, the term wild cucumber refers to plants in the genera Echinocystis and Marah, though the two are not closely related.