The term for pieces of information or facts that the writer wants the reader to know is "key points."
The term you are referring to is "key information" or "essential details." These are pieces of information or facts that the writer includes in a text to ensure the reader understands the main points being discussed. The purpose of including key information is to provide clarity and support the writer's argument or message.
The term you are looking for is "expository information" or "expository facts."
