In Summary

Usul al-Fiqh is defined as:

مَعْرِفَةُ الْقَوَاعِدِ الْعَامَّةِ الَّتِي تُسْتَخْدَمُ فِي اسْتِنْبَاطِ الْأَحْكَامِ الشَّرْعِيَّةِ الْعَمَلِيَّةِ مِنْ أَدِلَّتِهَا التَّفْصِيْلِيَّةِ

“Knowledge of the general principles which are utilised in deducing practical Shari’ah rulings from detailed evidences.”