An Upwork invoice is the document Upwork generates automatically for each hourly billing week, released milestone or bonus, issued in the freelancer's or agency's name to the client, with a matching invoice from Upwork for its own fees.
Freelancers on Upwork do not write invoices. When a weekly billing cycle closes on an hourly contract, or a milestone is released on a fixed-price one, Upwork raises an invoice from the freelancer to the client for the gross amount, and a separate invoice from Upwork Inc. to the freelancer for the service fee, and to the client for any client fees. All of them sit in the account's transaction history, downloadable as PDF, with the contract, the hours or milestone, the dates and any tax applied.
The split matters for bookkeeping. The freelancer's income for accounting purposes is the gross amount on the client invoice, and the service fee is an expense evidenced by Upwork's invoice, not a deduction from revenue. Clients likewise book the freelancer's invoice and Upwork's fee invoice separately. Where Upwork is required to collect VAT, GST or sales tax on its fee, that appears on Upwork's invoice, which is why the tax forms on the account matter.
A common request from clients is a custom invoice with their purchase order or company details. Upwork lets both sides add some details to their profiles that print on the invoice, but the document itself is Upwork's and cannot be replaced with one of the freelancer's own, because the payment runs through Upwork. For agencies, invoices are issued in the agency's name and the agency financial account receives the funds.
How Upwork Insights uses it
This term describes Upwork's own rules or product rather than a figure the index measures; the pages that do carry live figures are the stats and rate pages.