C ++: Valid but undefined state. What does it mean?

I am trying to understand std :: move. This document describes it well. But he says in the example section "..... while the bar loses its meaning and is now in a valid but unspecified state .....". Many other documents also use this terminology in the same context. Also, I found many answers on stackoverflow related to it. This question is exactly the same question. But he doesn't say, "What does unspecified mean?"

So my questions?

What does valid but unspecified mean?

What will be its effect on the pointer variable ( ClassA* ptr

)?

And what will be the effects on the object pointed to by the variable?

Thank.