What term means a sentence does not express complete thought?

The term for a sentence that does not express a complete thought is fragment.

Here's why:

* Sentence: A sentence must have a subject (who or what is doing the action) and a verb (the action itself).

* Fragment: A fragment lacks either a subject, a verb, or both.

For example:

* Complete sentence: The dog barked loudly. (Subject: dog; Verb: barked)

* Fragment: Barking loudly. (Missing subject)

* Fragment: The dog. (Missing verb)