A form of currency used by David to pay for his first wife Michal. As explained in 1 Samuel 18:25-27
of the Bible
, Saul's asking price was 100 foreskins. David was feeling generous and paid twice the asking price.
1 Samuel 18:25-27
Saul replied, "Say to David, 'The king wants no other price for the bride than a hundred Philistine foreskins, to take revenge on his enemies.'" Saul's plan was to have David fall by the hands of the Philistines. When the attendants told David these things, he was pleased to become the king's son-in-law. So before the allotted time elapsed, David and his men went out and killed two hundred Philistines. He brought their foreskins and presented the full number to the king so that he might become the king's son-in-law. Then Saul gave him his daughter Michal in marriage.
(The New International Version)