Entomology definition of Segment: a ring or division bounded by incisions or
sutures: a segment of an insect or of any articulate is a
transverse portion reaching entirely across the body, originally
separated on the exterior by incisions or sutures from the
preceding and the succeeding segments, having attached to it not
more than one pair of ventral appendages, containing internally
not more than one pair of nerve ganglia which supply nerves to
the pair of appendages; = somite, arthromere: fusion of segments
frequently obscures, as in the head: externally the walls of one
segment may be composed of a number of sclerites separated from
each other by secondary sutures.