The reverse of normalization. You normalize by moving redundant or non-related columns into other tables. For instance, instead of having a table with (cart id,

The reverse of normalization. You normalize by moving redundant or non-related columns into other tables. For instance, instead of having a table with (cart id, product id, price) you'd normalize by creating (cart id, product id) and (product id, price) tables. The (product id, price) table is a single source of truth, and, now, no matter what cart something is in the price is known to be correct (or as correct as the product price table). And updating a price means one edit, not many edits. Denormalization takes that normalized form and reverses it. Often for performance reasons. If updating prices is a rare occurrence, for this example, then getting the price total for a cart is slowed by forcing an extra join. Denormalizing brings the price back into the (cart id, product id, price) table and now the total price of a cart is a single query, no joins required.