Definitions for "Main idea"
The part of the paragraph or paper to which all the other ideas relate. See topic sentence and thesis.
a complete thought (a sentence) which expresses the most important idea of a passage
In informational or expository writing, the most important thought or overall position. The main idea or thesis of a piece, written in sentence form, is supported by details and explanation. See Theme, Thesis
Keywords:  told, heard, you're, tell, saying
Have you ever heard the saying, Tell them what you're going to tell them — Tell them — Then tell them what you told them