What is the difference between a bisector and a perpendicular bisector?

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)##.