A cash was a type of coin of China and East Asia from the 2nd century BC until the AD 20th century. The photograph to the right shows replicas of various ancient to 19th century cast coins in various metals found in China and Japan.

Terminology
The English word "cash", meaning "tangible currency", is an older and unrelated word from Middle French caisse.
 
There are a variety of Chinese terms for cash coins, usually descriptive and most commonly including the character qián meaning "money." Confusingly, Chinese qián is also a weight-derived currency denomination in Chinese called mace in English.
 
Manufacture
Traditionally, Chinese cash coins were cast in copper, brass or iron. In the mid-19th century, the coins were made of 3 parts copper and 2 parts lead. Cast silver coins were periodically produced but are considerably rarer. Cast gold coins are also known to exist but are extremely rare.
 
History
Chinese cash coins originated from the barter of farming tools and agricultural surpluses. Around 1200 BC, smaller token spades, hoes, and knives began to be used to conduct smaller exchanges with the tokens later melted down to produce real farm implements. These tokens came to be used as media of exchange themselves and were known as spade money and knife money.
 
As standard circular coins were developed following the unification of China by Qin Shi Huang, the most common formation was the round-shaped copper coin with a square or circular hole in the center, the prototypical cash. The hole enabled the coins to be strung together to create higher denominations, as was frequently done due to the coin's low value. The number of coins in a string of cash (yiguànqián) varied over time and place but was nominally 1000. A string of 1000 cash was supposed to be equal in value to one tael of pure silver. A string of cash was divided into ten sections of 100 cash each. Local custom allowed the person who put the string together to take a cash or a few from each hundred for his effort (one, two, three or even four in some places). Thus an ounce of silver could exchange for 970 in one city and 990 in the next. In some places in the North of China short of currency the custom counted one cash as two and fewer than 500 cash would be exchanged for an ounce of silver. A string of cash weighed over ten pounds and was generally carried over the shoulder. (See Hosea Morse's "Trade and Administration of the Chinese Empire" p. 130 ff.) Paper money equivalents known as flying cash sometimes showed pictures of the appropriate number of cash coins strung together.
 
The Koreans, Japanese, and Vietnamese all cast their own copper cash in the latter part of the second millennium similar to those used by China.
 
The last Chinese cash coins were struck, not cast, in the reign of the Qing Xuantong Emperor shortly before the fall of the Empire in 1911. The coin continued to be used unofficially in China until the mid-20th century. Vietnamese cash continued to be minted to 1933.
 
Inscriptions and denominations
The earliest standard denominations of cash coins were theoretically based on the weight of the coin and were as follows:
 100 grains of millet = 1 zhu
 24 zhu = 1 tael (liang)
 
The most common denominations were the ½ tael (bànliang) and the 5 zhu (wu zhu) coins, the latter being the most common coin denomination in Chinese history.
 
In AD 666, a new system of weights came into effect with the zhu being replaced by the mace (qián) with 10 mace equal to one tael. The mace denominations were so ubiquitous that the Chinese word qián came to be used a the generic word for money.  Other traditional Chinese units of measurement, smaller subdivisions of the tael, were also used as currency denominations for cash coins.
 
A great majority of cash coins had no denomination specifically designated but instead carried the issuing emperor's era name and a phrases such as tongbao  meaning "general currency" or zhòngbao meaning "heavy currency."
 
Coins of the Qing Dynasty (1644–1911) generally carried the era name of the emperor and tongbao on the obverse and the mint location where the coins were cast in Manchu and Chinese on the reverse.