When you hear the term "virtual currency" you probably think of fake money that holds no value. However, that's definitely not the case.
For World of Warcraft, Gold has always had real-world value, and actually a surprising amount of it. More recently, when Blizzard added the option to trade Gold for monthly subscriptions, its value not only became less volatile but also far more legitimate.
Actually, right now a single subscription token (30 days of playtime) is worth 208,722 Gold. In comparison, the one US dollar is currently worth 69,910 Venezuelan Bolivar.
In other words, World of Warcraft virtual currency is worth more than seven times Venezuela's cash.
With this in mind, it's no wonder why there are hundreds of gold-farming agencies in countries around the world. In places like Russia and China, you can find operations with thousands of employees responsible for farming and trading the virtual currency.
The video below, while long, offers great insight into the gold farming industry.