Blockchain is a type of shared database that differs from a regular database in how it stores information; Blockchains store data in blocks, which are then linked to each other using cryptography.
A hard fork refers to a radical change in the protocol of a blockchain network that effectively results in two branches, one following the previous protocol and one following the new version.
Hyperledger is an open source community dedicated to developing a set of stable frameworks, tools and libraries for permissioned enterprise-grade blockchain deployment.
Hyperledger composer is a business-oriented set of tools for creating enterprise blockchain applications under the auspices of the Hyperledger project.