Wikipedia
Apabhraṃśa
Apabhraṃśa (, , Prakrit: ) is a term used by vyākaraṇin (grammarians) since Patañjali to refer to the dialects prevalent in the Ganges (east and west) before the rise of the modern languages. In Indology, it is used as an umbrella term for the dialects forming the transition between the late Middle and the early Modern Indo-Aryan languages, spanning the period between the 6th and 13th centuries CE. However, these dialects are conventionally included in the Middle Indo-Aryan period. in Sanskrit literally means "corrupt" or "non-grammatical language", that which deviates from the norm of Sanskrit grammar.
Apabhraṃśa literature is a valuable source for the history of North India for the period spanning the 12th to 16th centuries.