It's an old English term for two farthings, a half penny, but it is often called a "ha' penny," which is pronounced "haypenny." See the Related Link.
the river Liffy and the Haypenny bridge and O connoll st. (and more recently the spire landmark)
It is worth as much as a buyer is willing to pay for it!
The archaic slang name for a halfpenny is "haypenny." It was used in British English, especially in older times when halfpennies were more commonly used as currency.
The UK currency was decimalised in 1971. The pound sterling is still being used and has been in use for several hundred years. Before 1971, there were 240 pennies in a pound and the name 'pound' was used because 240 copper pennies weighed one pound. Other coins in use before 1971 were a farthing (quarter of a penny), halfpenny (pronounced haypenny), threepenny (pronounced thri pence), sixpence (usually called a tanner), shilling (usually called a bob), two shillings (properly called a florin but known as two bob), half-crown (value two shillings and six pence) - crowns were withdrawn about 100 years ago. There were also ten shilling notes and one pound notes. Higher value notes remain the same.