This is the Lunar Calendar date for the Chinese Mooncake festival. Sometimes, it is also known as the Mid-Autumn Festival. It is believed that on this day, the moon is the biggest, roundest and brightest!
I came across a much funnier meaning today though. We were at Ming Court (famous breakfast venue in Ipoh) for Dim Sum when one of the waitresses said to me "You'd better sit further back in case somebody accidentally kicks your chair. It will give your 15 August a good bump" HUH?? What was she talking about???
My BEHIND! Bum. Butt. Backside. Derriere. Rear-End. Now you can add '15 August' to it. If you want to say it in Cantonese, "Bat Yuet Sap Mm"
By the way, here is the Latin way to say '15 August': 'Nates'.