"Double-Spending Bitcoin" Is a glitch into the bitcoin blockchain. Its basically a process of making someone ( like a merchant ) believe that you have send them the funds when you actually didn't. This can really be used to manipulate a lot of major websites like the gambling website : Anonymous Casino
Only a hand-full know!
This is not being talked in the bitcoin community due to not much knowledge about this. Moreover, this can happen due to people not wanting others to share their Double-Spend method as people will use a lot of bitcoin to double spend. Glass Hunt Hackers have been interviewed by Dash-Digital Cash in where they talk about this and they show you how you can do it yourself!
This video shows and explains how you can perform this double spending bitcoin procedure very easily.
Few Thousand per day!
Only a few thousand dollars worth of BTC are being Double-Spent each day in order to trick the merchant. This can easily be done by anyone with an access to the internet. Its not very ethical, but sending 1BTC somewhere like a casino easily doubling your money ( without any risk ) its a gamblers dream. You are able to perform this using this Double-Spending trick!
~Andrei