Parachain

A parachain is an application-specific chain connected to Polkadot's relay chain (or to Kusama, its canary network). Parachains produce their own blocks through collators, but relay-chain validators check those blocks and finalise them, so every parachain inherits the same pool of staked security. Messages and assets travel between parachains through the XCM format.

Access to that security used to be rationed through slot auctions: projects locked DOT, often raised from supporters in crowdloans, to lease a slot for up to two years. Polkadot later replaced the lease model with agile coretime, where teams buy blockspace on a core for a period, or on demand, which lowers the cost of launching a chain.

Being a parachain does not make a project safe or successful; it only guarantees that its blocks are validated by the relay chain. The application logic, the bridge to outside networks and token economics remain the team's responsibility. Older articles about crowdloans and auction winners describe a model that no longer applies to new chains.