ECM vs jamming

ECM and jamming both are nouns.

Word	Noun	Adjective	Verb	Adverb
ECM	Yes	No	No	No
jamming	Yes	No	No	No

As nouns, jamming is a hyponym of ECM; that is, jamming is a word with a more specific, narrower meaning than ECM:

ECM: electronic warfare undertaken to prevent or reduce an enemy's effective use of the electromagnetic spectrum
jamming: deliberate radiation or reflection of electromagnetic energy for the purpose of disrupting enemy use of electronic devices or systems

Other hyponyms of ECM include electronic deception, electronic jamming, jam.

ECM (noun)	jamming (noun)
electronic warfare undertaken to prevent or reduce an enemy's effective use of the electromagnetic spectrum	deliberate radiation or reflection of electromagnetic energy for the purpose of disrupting enemy use of electronic devices or systems