If you create a database report which has parameters each parameter should show its description as a tooltip.
In earlier versions this worked, but seems to be broken since the bootstrap update.
Navigate to http://localhost:8980/opennms/report/database/reportList.htm
and select a report.
The issue here is, that the custom tooltip tag I wrote awhile ago does not seem to work anymore with bootstrap.
Either fix that or use bootstrap build in internals instead.