Bitcoin is an open monetary network that lets participants verify and transfer a scarce digital asset without one company controlling the ledger.
The network is software run by independent nodes. The asset, bitcoin, is the unit recorded by that network. Exchanges, wallets, and ETFs are access layers around Bitcoin; none of them is the network itself.
Bitcoin does not promise a stable price, guaranteed profit, anonymous use, instant settlement in every situation, or protection from user error. A useful beginner definition includes both the capability and the limits.