I got the definition from PC world.

(Operational Data Store) A database designed for queries on transactional data. An ODS is often an interim or staging area for a data warehouse, but differs in that its contents are updated in the course of business, whereas a data warehouse contains static data. An ODS is designed for performance and numerous queries on small amounts of data such as an account balance. A data warehouse is generally designed for elaborate queries on large amounts of data.