Buddhist Hybrid Sanskrit (BHS) is the language in which most of the Mahāyāna Buddhist Sutras, such as the Perfection of Wisdom literature, were written.

BHS is a Middle Indo-Aryan language, a "Prakrit", to which have been added superficial elements designed to make the language resemble classical Sanskrit. Thus, while a BHS text will look like a Sanskrit text, it will obey slightly different rules, and feature grammatical and lexical innovations not found in the Sanskrit corpus proper.

Further Reading:

Edgerton, Franklin: Buddhist Hybrid Sanskrit Grammar and Dictionary.