Please define key terms

Thanks for this great project! I truly appreciate your ARCHITECTURE document but I am unclear on the definitions for a number of terms. Could you provide definitions and examples for the following terms:

* Activate
* Specification
* Requirement
* Possibility

In addition, can you clarify whether a `PossibilitySet` is a group of versions of the same artifact, with each version having the same transitive dependencies each with the same version range?

Start with the ARCHITECTURE document and trace how Activate, Specification, Requirement, Possibility, and PossibilitySet are used in the project. Done means the document defines each term with an example and clearly explains whether a PossibilitySet groups versions with matching transitive dependency version ranges.

Written by the indexing model from the issue text.