With the bitcoin source code freely available, it wasn't long before someone made a copy and created their own coin. This then led to the era of alternative coins, known as altcoins.
The bitcoin source code has been copied or "forked" 19,358 times thus far. This doesn't mean there are 19,358 different altcoins because many forks will be from people wanting their own copy to learn from or experiment with. As an indication of the active altcoins, there are just over 800 listed at coinmarketcap.com.
Forking: A technical term that programmers use when copying code from one application to another. This means the developer does not have to start from scratch.
There are some purists, or bitcoin maximalists, who see bitcoin ...