A syllable coda is the constituent following the syllable nucleus within a syllable. It can contain one or more consonants, or be absent. A syllable with a coda is conventionally called closed; one without a coda is open. These labels concern syllable organization, not whether the speaker's mouth is literally open.[ref]
Essentials of Linguistics (2nd edition) by Catherine Anderson and others. §3.10, codas and open/closed syllables
In “cat”,
[t] is the syllable coda; in “cats”, [ts] forms a final consonant cluster. The pronunciation of “see” has no coda in this analysis, despite its final written letters. Comparing these examples separates the acoustic sequence and its phonology from orthography. New to topics? Read the docs here!