A pickled cucumber (commonly known as a pickle in the United States and Canada or generically as gherkins in the United Kingdom, Ireland, Australia, and New Zealand).
It is a cucumber that has been pickled in a brine, vinegar, or other solution and left to ferment for a period of time.
This is done by either immersing the cucumbers in an acidic solution or through souring by lacto-fermentation.

Can guinea pigs eat dill pickles?