Vectorization is a process of converting database entity representation into a set of simple geometry primitives that could be used for rendering, exporting, etc. For example, a circle entity could be converted into a set of line segments, text could be tessellated into a set of triangles, etc.
Exploding is a process of subdividing database entities into simpler database entities. For example, a custom entity with text and circle geometry could be exploded into circle and text entities, but the explosion process does not change the type of entity geometry. For example, a circle and text cannot be exploded further because they are the simplest primitives themselves.