Plumb pudding theory, better known as Thomson model of an atom was the very fist model to describe electrons in an atom.
In this model, an atom consists of blob of positive charged substance and the electrons uniformly distributed within it.
The theory has last for only 5 years and was by disproved by Rutherford interpretation of the gold foil experiment which implied a very small nucleus of the atom containing a very high positive charge.
Since then, much better theories have been developed. Basically, we have switched from the pudding blob to a concetrated nucleus and an electron cloud: