Connotation is the set of associations, emotions, and implied meanings a word carries beyond its literal sense. Poets choose words for connotation as much as for dictionary meaning, because a single word can suggest mood, tone, history, class, age, danger, tenderness, or other shades of feeling.
It differs from denotation, which is the word's direct, literal meaning.
Example
Cold moon
silvered the empty yard;
her voice said "home,"
and the word itself felt warm.
Dylan Thomas's "Do Not Go Gentle into That Good Night" includes intensely connotative language, as in these lines:
Do not go gentle into that good night,
Old age should burn and rave at close of day;
Rage, rage against the dying of the light.