Bitcoin (with a capital B) is free open source computer software used for creating and maintaining the Bitcoin blockchain. The Bitcoin blockchain stores the world’s first and most popular cryptoasset known as bitcoin with a lowercase b. When a person downloads the Bitcoin software on their computer or smartphone, they can then send and receive “bitcoins” (with a lowercase b), which are the currency or units of exchange for the network created by computers running the Bitcoin software.
When a person owns bitcoin, they do not own a physical coin, nor do they own some sort of digital coin that they download to their computer, they own an exclusive association to specific entry on a single, distributed, worldwide ledger known as the Bitcoin blockchain. They can prove their exclusive association to this ledger entry, or “transaction” using cryptography. This ability to prove association to transactions on this ledger allows for a person to exclusively “own” bitcoin on the shared bitcoin blockchain. Everyone in the world can view and verify this ownership.