“A system without any central point of control is referred to as being decentralized. Bitcoin is designed to avoid having a central point of control, or more precisely a central point of censorship. Decentralization is a means to achieve censorship resistance.
There are two major aspects of decentralization in Bitcoin: miner decentralization and full node decentralization. Miner decentralization refers to the fact that transaction processing isn’t performed nor coordinated by any central entity. Full node decentralization refers to the fact that validation of the blocks, i.e. the data that miners output, gets done at the edge of the network, ultimately by its users, and not by a few trusted authorities.”