A (segment) bisector is any segment line or ray that splits another segment into two congruent parts.
For example in the picture if ##bar(DE)congbar(EB)## then ##bar(AC)## is the bisector of ##bar(DC)## since it split it into two equal sections.
A perpendicular bisector is a special more specific form of a segment bisector. In addition to splitting another segment into two equal parts it also forms a right angle (90) with said segment.
Here ##bar(DE)## is the perpendicular bisector of ##bar(AC)## since ##bar(AC)## is split into two congruent segments##bar(AE)## and ##bar(EC)##.