Proposal for major revision of metric definition

[mhebrard]

• Please check if the PR fulfills these requirements

• [x] You have a descriptive and meaningful commit message.

• [ ] Tests for the changes have been added (for bug fixes/features)

• [x] Docs have been added / updated (for bug fixes / features)

• [ ] You have done your changes in a separate branch. Branches MUST have descriptive names that start with either the fix/ or feature/ prefixes. Good examples are: fix/signin-issue or feature/issue-templates.

• [ ] You have commented the code, particularly in hard-to-understand areas

• What kind of change does this PR introduce? (Bug fix, new feature, docs update, ...) Major revision of the metric definition document (markdown)

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?) No breaking changes

• Other information:

[mhebrard]

TODO

• [x] re-order and re-format terminology & references
• [x] hamonize the metric definitions