What exactly is a Type II Error

I'm wondering what is the actual definition of a Type 2 Error?

For example:

In a hypothesis test, if I fail to reject the null hypothesis this is clearly not the same as accepting the null hypothesis. I am merely saying that I don't have enough evidence to say the null hypothesis is not true.

"Absence of evidence is not evidence of absence".

The question I ask is when is a type 2 error committed?

Is it committed when I fail to reject the null hypothesis or is it committed when I accept the null hypotheis or could it even be that both situations are true?

Thanks.