Is it hard to tell what someone is saying? Can you not see something clearly? Anything hard to make out is indistinct.
Indistinct things are fuzzy, unclear, and hard to see or understand. A whisper can be indistinct. A clear, confident speaker is not indistinct. People like to say what a cloud is shaped like, but clouds are generally pretty indistinct — that's why different people will see different shapes in the same cloud. When we're writing, speaking, or drawing, we should try to be distinct, not indistinct — because we want to be understood.