Bitcoin is money on the internet.
In the same way a country might decide to issue a money, the internet issued a money in January 2009.
This does beg the question, who has the authority to issue a money for the internet. The answer is a curious no-one and everyone. No-one is in charge but any one can participate, over time the more people that join in the more value and options for use accrue to the bitcoin network and it's users.
Bitcoin exists as a purely voluntary alternative money, issued on the internet by anyone who agrees to follow a set of rules. Likewise, it can be used by anyone on the internet who cares to follow the rules.
When you need it, it will be there, it doesn't take off holidays and weekends, it doesn't ask you invasive personal questions about what you've been up to and it doesn't even mind if you live under a restrictive fascist regime that doesn't want you to be bale to save up money.
The rules are pretty simple:
There will only be ~21 million bitcoin issued in total.
You can only issue bitcoins to if you win the mining lottery, which happens every ~10 minutes.
You can only spend money you own.
You can only spend the money once, no backsies.
There is no-one in charge, who gets to bend the rules to their liking.
Everyone is equal on the network.
All free, all open source and all running 24x7 for over 12 years :)