It's an ad agency term. "Traffic" is the person who coordinates the movement of the work between departments (e.g., account managers, creatives, designers, proofreading, studio, clients, printers, publications) and does his/her best to see that each job or phase of a job goes through each department on schedule. So in last night's case, she was there because the other departments were there working on a job, and she had to "ride herd" on it. Questions and concerns are channeled through traffic so that the various people involved in a job aren't constantly running back and forth between departments. For instance, if I have questions on something I've proofread (something I'm notorious for!), she resolves them through the account manager, writer, designer, etc. These days, some of this is done through a computerized system. My stuff is often handled manually, though, as there isn't an efficient way to digitally mark up layouts. The main tool of my trade is the (dreaded) red pen. (You'd love my "Don't Make Me Get Out My Red Pen!" t-shirt, with the apostrophe marked in red!)