It basically means going over 15 syns a day if you have something that requires more syns going on like a family party - but you set the upper limit in advance, say 50 and when you reach them you switch to diet coke and step away from the buffet. It's basically a ways of still feeling like you're in control. Flexi-synnning is not to be confused with having more syns on day so less on other days to bring you back to 15x7 for the week.