Final answer:
The abbreviation indicating a loud dynamic level in music notation is 'ff,' which means 'fortissimo,' or very loud.
Step-by-step explanation:
The abbreviation that indicates a loud dynamic level in music is ff, which stands for fortissimo. Dynamic levels in music are notations used by composers to indicate the loudness or softness of a piece or section of music. The options given, pp, mp, ff, and mf, represent different dynamic levels. Specifically, pp stands for pianissimo (very soft), mp stands for mezzo-piano (moderately soft), ff stands for fortissimo (very loud), and mf stands for mezzo-forte (moderately loud).