Attributed Revenue
Invoiced revenue credited to a marketing source.
Attributed revenue is invoiced revenue that Ghost could credit to a marketing source. Revenue means invoiced — one definition, used on every page.
Why it is lower than your total revenue
Total revenue is everything you invoiced. Attributed revenue is the part Ghost can trace back to a source: the chain from enquiry to booking to invoice has to be intact, and the enquiry has to have had a source.
The difference is not missing money. It is money whose origin Ghost cannot prove.
Timing
An invoice is credited in the period it was invoiced, to the channel that produced the original enquiry — which may have been months earlier. A period can therefore show revenue from leads that are not in that period's lead count. Both numbers are correct; they are answers to different questions.