Question

What was Apabhramsha?​

Answer 1

In Indology, it is used as an umbrella term for the dialects forming the transition...

Apabhramsa in Sanskrit literally means "corrupt" or "non-grammatical language", that which deviates from the norm of Sanskrit grammar.

Answer 2

$\huge \fbox \red {answer}$

Apabhraṃśa is a term used by vyākaraṇin since Patañjali to refer to languages spoken in North India before the rise of the modern languages.