According to the PMBOK® Guide (6th Edition), specifically within the Manage Project Knowledge process, knowledge is split into two distinct categories: Explicit and Tacit.

Tacit Knowledge: This is personal knowledge that is difficult to articulate or codify. It includes beliefs, insights, experience, " know-how, " and Expert Judgment. It is stored within the minds of individuals and is typically shared through conversations, shadowing, and interpersonal interaction.

Explicit Knowledge: This is knowledge that can be codified using symbols such as words, numbers, and pictures. It can be easily documented and shared.

Why Expert Judgment is Tacit Knowledge: Expert judgment relies on the specialized knowledge or expertise of an individual or group. It is built through years of experience and involves intuition and professional " gut feeling " that cannot be fully captured in a manual or a database. When a project manager consults a subject matter expert, they are tapping into that expert ' s tacit knowledge.

Analysis of Distractors:

A (Risk register): This is a formal document that records identified risks and their characteristics. Because it is written down and stored in a database, it is Explicit Knowledge.

B (Project requirements): These are documented descriptions of what is needed for the project. Since they are codified in a Requirements Documentation or Traceability Matrix, they are Explicit Knowledge.

D (Make-or-buy analysis): This is a specific tool/technique (often resulting in a documented decision) used to determine whether work can be accomplished by the project team or should be purchased from outside sources. The resulting data and criteria are Explicit Knowledge.