In computer science, distributed topology or computing is a form of decentralization which avoids bottlenecks and single points of failure by making the nodes in the network interchangeable. In the case of a pseudonymous routing network, the individual relays are even agnostic to both content and destination of messages travelling over it.
Unfortunately "distributed" is frequently confused with decentralized — so expect to encounter projects that claim to be a "distributed social network" when they are actually decentralized by mere federation like PSYC1 or XMPP. For reasons of privacy and better scalability it is however absolutely favourable to aim for distributed architectures like PSYC2 as explained in several pages linked here.