TWikiPackage: any functional Twiki build. (a generic term)
TWikiKernel: 1.the minimum functional TWiki build possible. 2.the minimum set of code, templates and docs required to produce a working TWiki (one skin, very few docs)
TWikiCore: The core code, eveyrthing under lib/TWiki but not including any Plugins or Contrib (only those components that are required by EVERY TWikiPackage
TWikiExtension: plugins, addons, contributed code, skins, webs, etc.
TWikiDistributionPackage: 1. a TWikiModule combined with a TWikiKernel packaged for install upon a specific platform: 2.a full twiki "kit" that "just works" out of the box on a specific platform for a specific task.
TWikiApplication: An integrated set of TWiki components, which may include webs, topics, TWikiForms, templates, html-forms, and formatted searches, that can be installed on top of a TWikiPackage to provides a specific functionality.