label vs tag

label and tag both are nouns.

Word	Noun	Adjective	Verb	Adverb
label	Yes	No	Yes	No
tag	Yes	No	Yes	No

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

label: an identifying or descriptive marker that is attached to an object
tag: a label written or printed on paper, cardboard, or plastic that is attached to something to indicate its owner, nature, price, etc.

Other hyponyms of label include gummed label, paster, sticker, ticket, title bar.

As verbs, label and tag are synonyms defined as:

Other synonyms of label include mark.

label (noun)	tag (noun)
an identifying or descriptive marker that is attached to an object	(sports) the act of touching a player in a game (which changes their status in the game)
a brief description given for purposes of identification	a game in which one child chases the others; the one who is caught becomes the next chaser
trade name of a company that produces musical recordings	a small piece of cloth
a radioactive isotope that is used in a compound in order to trace the mechanism of a chemical reaction	a label written or printed on paper, cardboard, or plastic that is attached to something to indicate its owner, nature, price, etc.
	a label associated with something for the purpose of identification

label (verb)	tag (verb)
distinguish (an element or atom) by using a radioactive isotope or an isotope of unusual mass for tracing through chemical reactions	provide with a name or nickname
distinguish (as a compound or molecule) by introducing a labeled atom	attach a tag or label to
assign a label to; designate with a label	touch a player while he is holding the ball
pronounce judgment on	supply (blank verse or prose) with rhymes
attach a tag or label to	go after with the intent to catch