Baloo is the file indexing and file search framework for KDE Plasma, with a focus on providing a very small memory footprint along with with extremely fast searching.
Baloo is not an application, but a daemon to index files. Applications can use the Baloo framework to provide file search results.
balooctl is a CLI command to perform certain operations on Baloo. The operations are indicated by arguments. All available arguments can be listed by issuing
balooctl --help in terminal app, such as userbase:Konsole.
To be noted, argument
checkDb is only meant to be used by developers for debugging. All it does is to print some messages but not to sanitize the database. And the execution time grows exponentially with the number of indexed files (see Comment 5 under bug #380465).