indentation vs blank space

indentation and blank space both are nouns.

Word	Noun	Adjective	Verb	Adverb
indentation	Yes	No	No	No
blank space	Yes	No	No	No

As nouns, blank space is a hypernym of indentation; that is, blank space is a word with a broader meaning than indentation:

indentation: the space left between the margin and the start of an indented line
blank space: a blank area

Other hypernyms of indentation include place, space.

indentation (noun)	blank space (noun)
the act of cutting into an edge with toothlike notches or angular incisions	a blank area
the space left between the margin and the start of an indented line
the formation of small pits in a surface as a consequence of corrosion
a concave cut into a surface or edge (as in a coastline)