Facelifts (if you're a first time Audi owner) are the subtle changes made to models (in between the complete makeovers that occur every 4 - 6 years) to ensure that new car buyers are getting the best shiny ever; this is easy enough as a marketing concept to understand because most new car buyers don't want to own last year's model.
Cars falling within a specific model span (indentified by version and chassis) can be more difficult to gauge as to whether they are "pre-face" or "facelift" models. The cosmetic stylings (apart from the invisible engineering changes) can be so subtle that only the owner will know. As an example, we provide this pictogram of the difference between the original Audi A5 and the Facelift Audi A5. You can nail this content down in 5 minutes and consider yourself an A5 B8 authourity.