Bitcoin Core is a software program that allows users to send and receive Bitcoin payments. It is a full-featured Bitcoin software that forms the backbone of the network, and it is the most trusted and widely-used Bitcoin software in the world. Bitcoin Core includes a built-in wallet, which allows users to store and manage their Bitcoin, as well as a built-in miner that can be used to secure the network by verifying transactions. It is an open-source software, which means that anyone can view and contribute to the source code. Bitcoin Core is available for free, and it can be downloaded and installed on a computer running Windows, Mac OS, or Linux.