Hi SITN- staple length? no idea!
Staple length is the length of each fibre. From the cut end to the tip. My own Castlemilk Moorits' fleeces are very very short, and it is this very short staple, rather than the softness, which makes them not a novice spin - and, when spun, not a strong yarn, unless mixed with some other, stronger fibre.
I'm still very much a novice spinner, and cannot at the moment make anything of my own CM fleece. So I am learning to blend, to card and to do 'woollen draw', all of which techniques I will need to use to process my own beautiful CM fleeces.