How far down do clouds come?

Question

when I like in the sky I see clouds and I was wondering how far down can a cloud form before its not "a cloud"

troposphere stratosphere if it gets below a certain point is it mist? or fog?

Answer 1

Cloud bases can come all the way to the ground at which point it is called fog.

Answer 2

A cloud is a cloud until it touches the ground then meteorologists would call it an "obstruction to vision" or fog.

Answer 3

Clouds will form at any level of the atmosphere where the humidity is 100%. As said by Geoff S, when the cloud reaches the ground its called fog.