Which of the following best defines a 'primary source'?

A primary source is a firsthand account produced during the time under study, which makes it a direct source of information about a particular event or period. Examples include diaries, photographs, letters, official documents, and artifacts. These sources provide original insights and perspectives that allow researchers to analyze and interpret the context and significance of historical events as they were experienced or recorded at that time.

In contrast, options such as a document created during a later time period do not qualify as primary sources since they are removed from the actual events they discuss. Likewise, summaries or compilations of several historical documents fall into the category of secondary sources, as they offer interpretations or analyses rather than original data. Therefore, the definition provided in the correct answer is consistent with the fundamental concept of what constitutes a primary source.