A skullcap can be :

• in anatomy, the top part of the skull
• as headgear, a type of cap
• Observant Jewish men wear yarmulkes, small cloth skull-caps
• Catholic clergy, including The Pope, wear skullcaps known as zucchetti.
• plants of the genus Scutellaria, such as s. lateriflora which is used in herbal medicine
• the autumn skullcap a poisonous mushroom
• Skullcap is the name of fictional ruins in the Dragonlance settings.