Form W-9
Given to a payer, not the IRS — it certifies that you are a US person and states your taxpayer ID.
Request for Taxpayer Identification Number and Certification. It never goes to the IRS: it goes to whoever is paying or holding money for you, so they can report correctly and decide whether to withhold. You certify three things — that the TIN shown is correct, that you are not subject to backup withholding, and that you are a US person. Expats meet it from an unexpected direction: under FATCA, a foreign bank that identifies US indicia on an account will ask for a Form W-9 so it can report the account, or for evidence that you are not a US person. Signing one is not optional paperwork; it is a certification of US status, and refusing to provide it usually results in backup withholding at 24% or the account being closed.
Related
This glossary entry is general reference, not advice for your specific return. Start your filing on the residency step.