Bitcoin is a cryptocurrency and worldwide payment system.
A user perspective, Bitcoin is nothing more than a mobile app or computer program that provides a personal Bitcoin wallet and allows a user to send and receive bitcoins with them. This is how Bitcoin works for most users.
It is telling that online crooks who launched the massive WannaCry ransomware attack earlier this year, which crippled part of the NHS and as well as businesses in 150 countries, demanded Bitcoin payments for organisations to regain access o their systems.