Yeah, until you hover over each of the Internal IDs, you wouldn't know which ones they are referring to.

@neerajrtiwari Always use data from Saved searches to build your csv update data. Since saved search will give you the internal id of the record use that value as the primary key for CSV import. For your custom form use the internal id for that form in your csv as the value for that field - in mapping click the small pencil icon and click the "internal id" radio button. This will make your csv import less error prone. I tend to use this mapping feature where ever possible.