What exactly is a DB Drain in ServiceNow platform?

[KarenFinlay]

What exactly is a DB Drain in ServiceNow platform?

ServiceNow Inc. has created various DB Drain change records for our instances in the past few months; however those are not accompanied by the usual KB Article with additional information; so I will like to know:
1. What exactly is DB Drain in ServiceNow platform?

2. What are the steps for ServiceNow DB Drain?

3. What is the end goal of the DB Drain?

[Mark Roethof]

The article you are sharing is about a different subject? "Tips for reducing instance database footprint"

[AshishKM]

Thanks for reviewing, updated that link with your one.