Final answer:
Prosody is the term that describes the rhythm and flow of language, in contrast to syntax which deals with the arrangement of words and morphology which is about the structure of words.
Step-by-step explanation:
The word that best fits the definition of rhythm and the flow of language is Prosody. Prosody refers to the rhythm, stress, and intonation of speech. It is the rhythm and cadence that poems and prose can take on, which can affect the linguistic musicality and emotive qualities of the language.
Meter is a specific component of Prosody associated with the length and rhythm of a poem. Syntax, however, is about the arrangement of words and phrases to create well-formed sentences, and Morphology refers to the structure of words and the way in which they are formed from phonemes and morphemes.