* Extensive research: Years of independent research culminating in a dissertation (or thesis), a substantial piece of original scholarly work that makes a novel contribution to the field.
* Advanced knowledge and expertise: A deep understanding of their subject area, far beyond what's required for a bachelor's or master's degree.
* Research methodology skills: Proficiency in designing, conducting, analyzing, and interpreting research.
* Critical thinking and problem-solving abilities: The ability to formulate research questions, evaluate evidence, and draw conclusions based on rigorous analysis.
* Communication skills: The ability to effectively communicate complex ideas, both orally and in writing, to both specialist and non-specialist audiences.
Essentially, a PhD holder is considered an expert in their field, capable of conducting independent research and contributing to the advancement of knowledge. The specific requirements vary slightly between universities and disciplines, but the core principles remain the same: original research, advanced knowledge, and scholarly contribution.