As MitchellRobert already pointed out, I'm refering to traffic in the sense of data traffic (commonly called bandwidth). A very common remark I've gotten is "but what about the bandwidth usage?!", but nowadays it's not hard to get a few terabytes of monthly traffic allowance for under $10.

For this particular VPS, I'm paying $9.30 a month, and it includes 2TB of montly traffic. Cheaper offers exist, and there are always providers like OVH that genuinely offer unmetered traffic on the cheap (as long as it's used for a legitimate purpose, eg. serving hosted files).

He's literally referring to bandwidth. Transit to get data from A (PDFy) to B (the visitor)

:-)