Original source drill-down 1 and Original source drill-down 2 are two analytics properties included on every contact record. Older HubSpot accounts may have the properties Original source data 1 and Original source data 2 instead, which contain the same information.
These drill-downs provide more insight on their original source (i.e., the contact's first visit or interaction with your business). Their values vary depending on the Original source property.
When viewing the Original source drill-down 2 property on a record, some values will appear with an infoinformation icon to show the internal value.