A knowledge object that provides data enrichment by mapping a select value in an event to a field in another data source, and appending the matched results to the original event. For example, you can use a lookup to match an HTTP status code and return a new field containing a detailed description of the status. The data sources for lookup content include search results,
.csv files, a KVStore collection, or a database connection.
For more information
In the Knowledge Manager Manual:
In the Developing Views and Apps for Splunk Web: