Answer: Osmosis
Osmosis is a process in, which molecules of a solvent passes through a semi-permeable membrane from a less concentrated solution to the more concentrated one. Osmosis is a process that can be observed when a cell interacts with it's external environment to maintain it's metabolism. The cell membrane of the cell acts as a selectively- permeable membrane, which allows certain solute and solvent molecules to enter or go out of the cell.
Raisin is a type of dry fruit, produced by the drying of grapes. In the given situation, the raisins swelled up due to osmosis. As, the water present in the glass, was able to pass through the external skin of grapes acting as a semi-permeable membrane. Hence, the raisins swelled up.