Bitcoin is money no one can take without your permission. It cannot be inflated away or confiscated, because no one person, company, or government controls it.
Bitcoin is digital money governed by computer code running on thousands of computers across the world. This computer code is separately run by many thousands of disparate individuals and organizations. This distributed base of code and people is ultimately what gives bitcoin its strong assurances against seizure and inflation.
Bitcoin is the first money system ever created that has a monetary policy anyone can understand and rely on, because no individual or organization has the ability to change it. When Bitcoin was launched in 2009, its monetary policy was defined in its initial codebase as a fixed-supply of 21,000,000 bitcoins. Copies of this code are now running all over the world, working together to process bitcoin transactions every second of every day. Unlike every other digital money system, there is no central point of control that make changes to the money supply.
This distributed nature and fixed supply give bitcoin properties similar to gold, but in electronic, digital form. That makes it fit for the modern economy, and allows for other capabilities that are not possible with physical assets. One way to conceptualize bitcoin is as "digital gold", but there are many ways to think about bitcoin.