The term 'the heart of the matter' is used to refer to the most important or essential part of a situation. GIST is an acronym for 'general idea, summary, and theme, ' which is a concise way of summarizing the main points of a text. NUB is an abbreviation for 'NUB of the matter, ' which is another way of saying the heart of the matter. BRASSTACKS is a phrase that means to tackle a problem head-on, without hesitation. Finally, NITTYGRITTY is an expression that refers to the details or specifics of a situation. All of these terms are related to the phrase 'the heart of the matter, ' as they all refer to the most important aspects of a situation.