To cut through some of the confusion surrounding bitcoin, we need to separate it into two components. On the one hand, you have bitcoin-the-token, a snippet of code that represents ownership of a digital concept - sort of like a virtual IOU. On the other hand, you have bitcoin-the-protocol, a distributed network that maintains a ledger of balances of bitcoin-the-token. Both are referred to as "bitcoin."
The system enables payments to be sent between users without passing through a central authority, such as a bank or payment gateway. It is created and held electronically. Bitcoins aren't printed, like dollars or euros - they're produced by computers all around the world, using free software.
It was the first example of what we today call cryptocurrencies, a growing asset class that shares some characteristics of traditional currencies, with verification based on cryptography.
Who created it?
A pseudonymous software developer going by the name of Satoshi Nakamoto proposed bitcoin in 2008, as an electronic payment system based on mathematical proof. The idea was to produce a means of exchange, independent of any central authority, that could be transferred electronically in a secure, verifiable and immutable way.
To this day, no-one knows who Satoshi Nakamoto really is.
In what ways is it different from traditional currencies?
Bitcoin can be used to pay for things electronically, if both parties are willing. In that sense, it's like conventional dollars, euros, or yen, which are also traded digitally.
But it differs from fiat digital currencies in several important ways: