Technically, sharding is a synonym for horizontal partitioning. In practice, the term is often used to refer to any database partitioning that is meant to make a very large database more manageable.

The governing concept behind sharding is based on the idea that as the size of a database and the number of transactions per unit of time made on the database increase linearly, the response time for querying the database increases exponentially. 

Additionally, the costs of creating and maintaining a very large database in one place can increase exponentially because the database will require high-end computers. In contrast, data shards can be distributed across a number of much less expensive commodity servers. Data shards have comparatively little restriction as far as hardware and software requirements are concerned.