فَصْلٌ: الْمَفْعُولُ الْمُطْلَقُ. وَهُوَ مَصْدَرٌ بِمَعْنَى فِعْلٍ مَذْكُورٍ قَبْلَهُ.
Translation: The absolute object is a verbal noun carrying the meaning of a preceding, explicitly mentioned verb.
A maṣdar names an action, such as ضَرْبٌ “striking”. In the common pattern it follows the verb as an accusative absolute object.