What do the raisins represent in the raisin pudding model of the atom?

The 'raisin pudding' model of the atom is more traditionally called the 'plum pudding model'.

The plums represented negatively charged corpuscles (electrons) surrounded by a positively charged pudding.

The plum pudding model became outdated in 1909 - 1911 when experiments showed that the positively charged atoms were extremely small.