Is there a specific definition on ESL?

Hi, recently i started thinking about ESL and the first question that came to mind was about the levels. It seems like each agency dedicated to teach ESL has its own Levels and i was wondering if there's a way to compare ESL to English, i.e. ESL Level 1 = Reading English at _____ grade level, speaking English at _______ grade level.

Is it really an equivalent English grade to every ESL level?

There's no standard- different places use different measures.