What is a group of words called that is not a sentence?

A phrase is not a sentence.

The Congressional Medal of Honor

America, the beautiful

recliner chair

Clauses are not sentences - they are missing subjects and verbs.

When you think about

On the way home

Calling them back

A sentence fragment, or an incomplete thought, is not a complete sentence.

Examples of incomplete fragments might include:

He. (the one Word nothingness; subject but no verb or object.)

Where the lives up in the treetops. (no subject; no object; needs more to answer "So?")

Are going. (Got the verb but no subject or object.)

Running. (Same.)

When you get here.... (A clause that is missing the rest of its thought.)

When you when where might you? (Scrambled eggs; lots of Words but it makes no sense!)

Have the then you felt best. (No subject; Incomplete thought; verb confusion; no object.)

In comparison, run-on sentences try to put too much and many distinct thoughts into one sentence, often with little punctuation. Often, run-ons switch verb tenses when it should stay with one verb tense. Run-ons forget that readers are not inside the writer's mind; we don't know what the writer was trying to say, and it's all jumbled together.

Example: Jon came running downstairs he was late then he ate a toaster waffle when he walked at school he saw his best friend.