Bitcoin Key Innovations

Bitcoin includes 4 key innovations that are brought together in a unique and powerful combination:

A decentralized peer-to-peer (P2P) network (the bitcoin protocol)
A public transaction ledger (the blockchain)
A set of rules for independent transaction validation and currency issuance (consensus rules)
A mechanism for reaching global decentralized consensus on the valid blockchain (Proof-of-Work algorithm)

(from Saylor Academy Course: Bitcoin for Developers Unit I)