# Altium trace length vs signal length

I've seen both of these in the PCB tab when editing the PCB board in Altium Designer.. what are the two?
I thought I new, but I have fully routed traces with signal lengths of 0 as well as signal and trace lengths that are totally different from each other. As well as sometimes signal lengths go up and down with the trace lengths as I'm routing, but other times the signal lengths do not change...

What are these two things, how are they related, and how do I edit signal lengths? (I'm assuming I'm right in thinking trace lengths are determined by the physically routed length of the traces. If not then please explain).

Thanks!