It is the amount of time when flavours persist and linger in the mouth after you have drunk or spat out the wine. It is timed in seconds. French call it “caudalie” with each “caudalie” being one second. The length of a wine is highly correlated to the quality of a wine, so the longer the length, the better the wine: 1 to 3 seconds: short to average length. 4 to 9 seconds: good to very good length. 10 and above: excellent to exceptional.