land site vs piece of land

land site and piece of land both are nouns.

Word	Noun	Adjective	Verb	Adverb
land site	Yes	No	No	No
piece of land	Yes	No	No	No

As nouns, piece of land is a hypernym of land site; that is, piece of land is a word with a broader meaning than land site:

land site: the piece of land on which something is located (or is to be located)
piece of land: an extended area of land

Other hypernyms of land site include parcel, parcel of land, piece of ground, tract.

land site (noun)	piece of land (noun)
the piece of land on which something is located (or is to be located)	an extended area of land