Definition & Meaning of "spend a penny"in English

What is the origin of the idiom "spend a penny" and when to use it?

The idiom "spend a penny" originates from British English and is closely associated with the concept of public restrooms, particularly pay toilets. The expression became popular in the mid-20th century when public toilets in the United Kingdom required a one-penny coin (a British penny) for access. To use these facilities, individuals had to "spend a penny" by inserting a coin into the turnstile or lock mechanism, allowing them entry. Over time, the term has extended beyond its literal meaning to indicate the need to urinate or use the toilet in a more general sense.