Oolong known as 'Wulong' in Mandarin are produced in China and Taiwan based on centuries old tradition and are very popular teas in these countries. Oolong teas are semi-oxidised, there are two types, some more green, rolled into balls and less oxidised which gives a sweeter flavour like green tea. The other oolongs are darker with more open leaves. These have been oxidised more which makes the tea more caramelly and fruity to taste. Once you experiment with an Oolong you won't be able to stop. Another superfood of tea with health research indicating decreased risk of heart disease and diabetes. In Asia, Oolong is an extremely popular drink to have after a meal to aid with digestion and bloatedness.
A quick cool story of where the name came from. Wulong means "black dragon", referring to the black snakes that coil around the tea bushes in the fields. Parents told the local kids they were little black dragons so they would not be scared.