Op-Up?
 

I'm sorry to ask such a stupid question - but what is an op-up? Is that when the airline offers a discounted rate to move up a class? Or a surprise (free) upgrade?

It's a free surprise upgrade usually as a result of Economy Class being oversold. Elite status helps.

Op-up is short for Operational Upgrade, normally refers to a complimentary upgrade to business/first when coach is oversold.

Ah - got it. I thought maybe it was 'opportunity' or 'optional' (which I took to mean pay for it at a lower rate than if you'd bought it with the new ticket).

Thanks for your help! We can let this thread slide off to oblivion now! ;)

fyi, there is a glossary under "help" at the very top of the page...