According to the Bible, Samson was given supernatural strength by God to fight his enemies, the Philistines, and perform heroic acts; but when he was tricked into allowing his hair to be cut by a Philistine woman named Delilah, Samson was powerless.
A lock of hair is a piece(s) of hair which has been cut from a human head, typically being held together in some manner.
This trinket is a reference to the effect of Bloody Lust (Samson's starting item) in the original game, which was later changed in Rebirth and added in Afterbirth as the item Lusty Blood.