An inactive sub can be inactive because they've been told not to move a muscle by their master, they've been completely bound a gagged by their master, or they're dead, quite possibly from the aforementioned gag being a bit too effective!
Whereas an active sub is very active as they're busy carrying out the orders of their master!
Oh wait....this isn't the Sadism & Masochism Forum is it?
Sorry my mistake.....wrong forum!