What is a sentence?
A sentence is a group of words that expresses a complete thought.
A complete thought is clear.
A sentence always begins with a capital letter.
It ends with a full stop (.), a question mark (?) or an exclamation mark (!).
Ted sent me a letter.
Jane slept soundly.
A sentence fragment does not express a complete thought.
The reader or listener cannot be sure what is missing in or the meaning of a sentence fragment.
He or she will be left wondering: What is this about? What happened?
Fragment: The huge boat.
Sentence: The huge boat sails down the river.
You can correct a sentence fragment by supplying the missing information.