The Head of Herbology is an illustrious title given to the teacher at Hogwarts School of Witchcraft and Wizardry in charge of the school's Herbology department, meaning that they are the Professor in said subject who enjoys the highest degree of seniority over other herbology professors and presumably the one setting up the curriculum.
During the 1990s, long-serving Herbology Professor Pomona Sprout served as the school's Head of Herbology.