How much is REALLY -24dBFS?

Hi!

I have made a recording with my 816x and it peaked at -24dB. So what does this tell me exactly? Is this -24dB ALWAYS the same? Or is it relative to something? If so, to what? Is it the same as if I would play a sine-wave at -24dB in Cubase? With the master volume on the 816 turned all the way up?

I would like to have this figure in dBu if possible.

Many thanks for ANY input here!


/R

He ya go: decibel