DSL vs telephone line

DSL and telephone line both are nouns.

Word	Noun	Adjective	Verb	Adverb
DSL	Yes	No	No	No
telephone line	Yes	No	No	No

As nouns, telephone line is a hypernym of DSL; that is, telephone line is a word with a broader meaning than DSL:

DSL: a generic name for digital lines that are provided by telephone companies to their local subscribers and that carry data at high speeds
telephone line: a telephone connection

Other hypernyms of DSL include line, phone line, subscriber line, telephone circuit.

DSL (noun)	telephone line (noun)
a generic name for digital lines that are provided by telephone companies to their local subscribers and that carry data at high speeds	a telephone connection
	the wire that carries telegraph and telephone signals