Is this a sentence fragment?
Smoke from the cabin visible for miles up and down the coast.
no yes
A sentence is a group of words that expresses a complete thought.
The band I'm in has been rehearsing daily because we have a concert in two weeks.
A sentence fragment is a group of words that does not express a complete thought.
Rehearsing daily because we have a concert in two weeks.
This fragment is missing a subject. It doesn't tell who is rehearsing.
The band I'm in.
This fragment is missing a verb. It doesn't tell what the band I'm in is doing.
Because we have a concert in two weeks.
This fragment is missing an independent clause. It doesn't tell what happened because of the concert.
This is a sentence fragment. It does not express a complete thought.
Smoke from the cabin visible for miles up and down the coast.
Here is one way to fix the sentence fragment:
Smoke from the cabin is visible for miles up and down the coast.