Permissionless
In short: Permissionless describes a system, most often a blockchain network, where no authority sets the rules for who can use it or how they can use it.
Permissionless describes a system, most often a blockchain network, where no authority sets the rules for who can use it or how they can use it. Anyone who follows the protocol's open rules can join, send transactions or help run the network.
Why it matters
Permissionless networks such as Bitcoin and Ethereum let anyone hold an address, run a node or build an application without asking for approval. This openness makes them hard to censor and lets new services build on each other freely. The flip side is that nobody screens participants, so users have to judge projects and counterparties themselves. Services that connect to these networks, such as centralized exchanges, can still set their own account rules, including identity checks.
Example
Anyone with an internet connection can download the software of a permissionless blockchain, run a full node and verify every block without registering. A developer can deploy a smart contract on a permissionless platform, and anyone can use it. A company ledger where only invited partners can read or write data is the opposite: a permissioned system.