Oolong teas are the most popular in China and Taiwan. These tea leaves undergo extensive processing which brings out complex layers of flavoring. They are neither green nor black teas and have a distinctive taste and aroma of their own. These leaves can be used more than once, and will often have different flavors with each brewing. The caffeine content of Oolongs tend to be rather high.
Huge congrats to MiniStuart for ftf and no hint!