output-to-input ratio vs ratio

output-to-input ratio and ratio both are nouns.

Word	Noun	Adjective	Verb	Adverb
output-to-input ratio	Yes	No	No	No
ratio	Yes	No	No	No

As nouns, ratio is a hypernym of output-to-input ratio; that is, ratio is a word with a broader meaning than output-to-input ratio:

output-to-input ratio: the output power of a transducer divided by the input power
ratio: the relative magnitudes of two quantities (usually expressed as a quotient)

output-to-input ratio (noun)	ratio (noun)
the output power of a transducer divided by the input power	the relation between things (or parts of things) with respect to their comparative quantity, magnitude, or degree
	the relative magnitudes of two quantities (usually expressed as a quotient)