parkland vs piece of land

parkland and piece of land both are nouns.

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

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

parkland: a large area of land preserved in its natural state as public property
piece of land: an extended area of land

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

parkland (noun)	piece of land (noun)
a large area of land preserved in its natural state as public property	an extended area of land