What is coin with a square hole in the middle?

The coin with a square hole in the middle is known as a Chinese cash coin. It is an ancient form of currency that was used in China for over 2000 years, from around the 7th century BC to the early 20th century AD.

The square hole in the middle of the coin serves a practical purpose - it allowed the coins to be strung together in piles of 1000 or more, making them easier to handle and transport.

Cash coins were made from a variety of materials, including bronze, iron, and even paper. They came in a range of denominations and were often decorated with various symbols or inscriptions that indicated their value or the era in which they were minted.

Today, Chinese cash coins are primarily used for decorative purposes or as part of traditional Chinese practices such as feng shui. They are also a popular item for collectors and can be found in antique shops and online marketplaces.