user vs end user

user and end user both are nouns.

Word	Noun	Adjective	Verb	Adverb
user	Yes	No	No	No
end user	Yes	No	No	No

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

user: a person who makes use of a thing; someone who uses or employs something
end user: the ultimate user for which something is intended

Other hyponyms of user include consumer, usufructuary, utiliser, utilizer, wearer, tweep.

user (noun)	end user (noun)
a person who makes use of a thing; someone who uses or employs something	the ultimate user for which something is intended
a person who uses something or someone selfishly or unethically
a person who takes drugs