GCE "o" level?
 

If I grew up in the US and obtained a BS and an MS, is there an equivalent for this thing in our education system that many asian airlines list?

High school graduation is about equivalent. Most countries don't require a degree to be a pilot however you have to demonstrate competency in the basics. You have an advanced degree so it's moot anyway. GCE O level stands for General Certificate of Education Ordinary Level. The next level is "A" for Advanced then on to University etc......