Glossary

Every term in the method, in one place. Terms link to the page that treats them fully.
Skill — the basic building block: one concrete, precisely named ability. Either no-level or three-level. (Chapter 2)
No-level skill (yes/no) — a skill small enough that you either know it or you don't; nothing meaningful to grade. Stored internally as level 0, which is never shown to users. (Chapter 2)
Three-level skill — a skill large enough to grow through stages: beginner → confident → expert, each level a prerequisite of the next. In a tree, each level is treated as a separate skill. (Chapter 2)
Beginner — knows the basics (fresh from a course or book); can do the work but needs help or a lot of documentation along the way. (Chapter 2)
Confident — hands-on experience; delivers most tasks alone, reaching for docs only on the less common parts. (Chapter 2)
Expert — considerable experience; handles almost everything without help, looking things up only for obscure cases. Confident enough to teach others. (Chapter 2)
Prerequisite — a skill required before another becomes learnable. Defined once, on the skill itself, at organisation level — never inside a tree. (Chapter 2)
No double-linking — the rule that every dependency is expressed once, at the closest link: if B needs A and C needs B, C connects through B, never also directly to A. (Chapters 2–3)
Granularity rule — a well-cut skill takes roughly one to three months to progress one step. Longer: split it. Nothing to grade: make it no-level. In doubt: aim bigger. (Chapter 2)
Tree — a scope of view over a connected subset of skills; an area of knowledge forming a logical part of a larger whole (e.g. Testing, Frameworks). (Chapter 3)
Root — a prerequisite of a tree's skills that isn't itself in the tree; surfaces beneath the tree as its entry requirement. Derived, never placed by hand. Applies at forest level too. (Chapter 3)
Forest — a group of trees: the full scope of knowledge for a single role, usually one forest per role covering every rank. (Chapter 4)
Rank — a seniority level tied to a person (junior / mid / senior by default), defined as a concrete set of skills at given levels within a forest. (Chapter 4)
Coverage — for a skill: how many people on a team hold it, and at what level. The first team-level read. (Chapter 8)
Gap — a skill the team needs but nobody holds, or holds only at beginner. (Chapter 8)
Single point of failure — a skill exactly one person holds at a usable level; a risk the moment that person is unavailable. (Chapter 8)
Skills heat map — a grid of team members against skills, with the level in each cell; the whole forest at a glance. (Chapter 8)
Skill champion — the named person for a critical skill who answers questions, mentors, and validates self-assessments. (Chapters 5, 8)
Teaching-back — explaining or teaching a skill to someone else; the method's favourite test for advancing to confident or expert. (Chapters 5, 7, 9)
Peer validation — the practice of levels being claims that colleagues confirm, keeping assessment honest at scale — especially once levels touch pay. (Chapter 5)
Forest review — the twice-yearly session that moves skills between ranks, retires outdated skills, and adds emerged ones. One year without it is the hard maximum. (Chapter 6)