Holds
An unsigned first-round pick charges the team's cap at 120% of his draft slot's rookie-scale salary (because first-rounders may sign for up to 120% of scale, and almost all do).
Second-round picks carry no hold. Pick holds count against the cap only and disappear when the pick signs, replaced by his actual rookie-scale contract.
See it live: pick any team and tap the numbers on its cap sheet.