The story
The electrons are viewed as negatively-charged "plums" in a positively-charged "pudding".
Etymology from Wiktionary, CC BY-SA 4.0.
plum pudding model
Today it means: An obsolete scientific model of the atom, devised shortly after the discovery of the electron but before the discovery of the atomic nucleus, and according to which the atom is composed of electrons surrounded by a soup of positive charge to balance the electrons' negative charges. It was disproved in 1909. Full definition →