Hop Projects are a conceptual grouping of configurations, variables, metadata objects and workflows and pipelines. Projects can inherit metadata from parent projects. A project contains one or more environments where the actual configuration is defined.
Example: a 'Sales' project contains a 'customers' database connection and a number of workflows and pipelines. The runtime configurations, database connection properties etc are defined in the 'dev', 'uat' and 'prd' environments.

Hop Environments are instances of projects that hold the actual runtime configurations and other metadata objects for a project.
Example: the 'dev' environment for the 'Sales' project specifies to read from host '10.0.0.1' for the 'customers' database connection