flight of steps vs staircase

flight of steps and staircase both are nouns.

Word	Noun	Adjective	Verb	Adverb
flight of steps	Yes	No	No	No
staircase	Yes	No	No	No

As nouns, staircase is a hypernym of flight of steps; that is, staircase is a word with a broader meaning than flight of steps:

flight of steps: a stairway (set of steps) between one floor or landing and the next
staircase: a way of access (upward and downward) consisting of a set of steps

Other hypernyms of flight of steps include stairway.

flight of steps (noun)	staircase (noun)
a stairway (set of steps) between one floor or landing and the next	a way of access (upward and downward) consisting of a set of steps