An object store raises the level of abstraction presented by today's block devices. Instead of presenting the abstraction of a logical array of unrelated blocks, addressed by their index in the array (i.e., their Logical Block Address (LBA)), an object store appears as a collection of objects. An individual object is a container of storage (object-data and object-meta-data) that exposes an interface similar to a file, and presents the abstraction of a sparsely allocated array of bytes indexed from zero to infinity.
The object store provides "fine-grain" object-level security, improved scalability by localizing space management, and improved management by allowing end-to-end management of semantically-meaningful entities.
A more in-depth description can be found at the following sites: