paraboloid vs plane figure

paraboloid and plane figure both are nouns.

Word	Noun	Adjective	Verb	Adverb
paraboloid	Yes	No	No	No
plane figure	Yes	No	No	No

As nouns, plane figure is a hypernym of paraboloid; that is, plane figure is a word with a broader meaning than paraboloid:

paraboloid: a surface having parabolic sections parallel to a single coordinate axis and elliptic sections perpendicular to that axis
plane figure: a two-dimensional shape

Other hypernyms of paraboloid include two-dimensional figure.

paraboloid (noun)	plane figure (noun)
a surface having parabolic sections parallel to a single coordinate axis and elliptic sections perpendicular to that axis	a two-dimensional shape