What is referred to as an original document containing firsthand observations and conclusions?

The correct answer is a primary source. A primary source is defined as an original document or artifact that provides direct evidence or firsthand accounts about a particular event or topic. Examples of primary sources include letters, diaries, interviews, original research reports, and historical documents. These materials are created by individuals who have directly experienced or witnessed the events being documented, making them invaluable for research as they offer insights and perspectives that are unmediated by interpretation or analysis from others.

In contrast, a secondary source interprets or analyzes primary sources. Secondary sources include textbooks, articles that summarize research findings, or critiques. An editorial reflects the opinions of the publisher or editor on a particular issue, while a research paper can be both primary or secondary depending on whether it presents original research or analyzes existing studies.