Difference blunder and mistake?

Can anyone tell me where the line is? When does a mistake become so bad it's a blunder?

A mistake is any bad move.

A blunder is something that loses material or leads to checkmate in very short order, but wasnt forced.

For example in my last game I had this position as white, and black did a terrible move:

Thats not a blunder. It doesnt lose material, and doesnt lead to checkmate. But its a big mistake because while now has an overwhelming advantage and black wasnt even forced to give white this advantage.

You could also say that blunders are the kind of mistakes a master should no longer make. Like in the most simple case moving a piece unprotected on a field thats under attack by the opponent.