What is the term for a statement that conveys the main idea or argument in a piece of writing?

The term that best describes a statement conveying the main idea or argument in a piece of writing is "thesis." A thesis statement typically presents the central argument or assertion that the writer intends to support and develop throughout the text. It serves as a roadmap for both the writer and the reader, clearly indicating what the paper will discuss and what position is being taken.

A thesis is usually specific and arguable, providing a foundation for the subsequent support and analysis presented in the body of the work. This distinction is important to differentiate it from other terms. For instance, while "claim" can refer to a specific assertion made within the text, it does not encompass the overall main idea as comprehensively as a thesis does. Similarly, "summation" refers to a summary of points rather than the initial assertion or argument, and "observation" pertains more to noticing facts or details without asserting them as overarching arguments. Thus, the thesis stands out as the core component that encapsulates the writer's primary focus.