to supply or provide a place with too much of something, creating a stock in excess of what is needed or wanted;
e.g. Some people like to overstock their pantry before a storm, so they are prepared in case they become stranded at home.
(noun)
an excess quantity or stock/supply of some goods such that the inventory exceeds requirements or demands, especially in the context of manufacturing or retailing;
e.g. Many furniture stores sell their overstock at steep discounts when the patterns become outdated.