A piedfort or piedforte is a coin of twice or more times the thickness of the currency coin, though often exactly twice the normal weight and thickness. They are normally struck for presentation purposes by mint officials, collectors or VIPs.
Great Britain is well known for creating many commemorative piedfort coins. Including many coins in the eighties and nineties.
The word "piedfort" is French and combines the two words "pied", meaning weight, and "fort", meaning strong or heavy; thus a piedfort is literally a "heavyweight" coin.