Nimbo-stratus and stratus clouds form at low altitudes.
fog
nimbostratus
something... :P
Means a cloud that's fairly close to the ground
Low or medium.
stratus
they are made of stuff
Cirrus clouds are high-altitude clouds.
I think it is a cumulonimbus.
low type
Yes. Alto clouds form the medium altitude group, but stratus clouds are at low altitudes.
Cumulonimbus clouds span the entire distance from low to high altitude, and so do not fit into any of the three height classifications.