bend vs concertina fold

bend and concertina fold both are nouns.

Word	Noun	Adjective	Verb	Adverb
bend	Yes	No	Yes	No
concertina fold	Yes	No	No	No

As nouns, concertina fold is a hyponym of bend; that is, concertina fold is a word with a more specific, narrower meaning than bend:

bend: an angular or rounded shape made by folding
concertina fold: a continuous parallel folding in an accordion-like fashion, that is with folds alternatively made to the front and back in zig-zag folds.

Other hyponyms of bend include plait, pleat, kink, twirl, twist, pucker, ruck, accordion fold, z-fold, zig-zag fold.

bend (noun)	concertina fold (noun)
curved segment (of a road or river or railroad track etc.)	a continuous parallel folding in an accordion-like fashion, that is with folds alternatively made to the front and back in zig-zag folds.
diagonal line traversing a shield from the upper right corner to the lower left
movement that causes the formation of a curve
an angular or rounded shape made by folding
a circular segment of a curve

bend (verb)	concertina fold (verb)
cause (an object) to assume a crooked or angular form
bend a joint
form a curve
change direction
turn from a straight course, fixed direction, or line of interest
bend one's back forward from the waist on down