main idea / central idea
main idea / central idea (idea principal / idea central)
the most important point the author makes about the topic, stated as a complete sentence.
Example
City trees cool streets and clean the air, but only if they are watered and protected. (A main idea: a full sentence about the topic.)
In Spanish
main idea / central idea (idea principal / idea central) — el punto más importante que el autor presenta sobre el tema, expresado en una oración completa.
City trees cool streets and clean the air, but only if they are watered and protected. (Una idea principal: una oración completa sobre el tema.)