database shard (sharding)
A database shard ("sharding") is the phrase used to describe a horizontal partition in a database or search engine. The idea behind sharding is to split data among multiple machines while ensuring that the data is always accessed from the correct place.
Since sharding spreads the database across multiple machines, the database programmer specifies explicit sharding rules to determine which machines any piece of data will be stored on.
Sharding may also be referred to as horizontal scaling or horizontal partitioning.