Transmittal
A cover document accompanying any set of drawings, submittals, or other project documents sent between parties, recording what was sent, to whom, when, and why, creating a paper trail independent of the documents themselves.
Why it matters
The document itself proves what was sent, but only the transmittal proves when it was sent and to whom, exactly the details a later dispute over timing or notice usually turns on.
On a real project
A general contractor sends a revised drawing set to a subcontractor with a formal transmittal recording the date, the specific revision number, and who received it, rather than an informal email with the files attached.
Who this matters most to
A Document Control Specialist issues and files every transmittal, maintaining the project's official record of what moved between parties and when.
Where this goes wrong
A revised drawing set gets emailed informally without a formal transmittal recording what was sent and when. Months later, during a dispute over which drawing revision a subcontractor was actually working from, there's no transmittal record to settle the question.