If people get down to the nitty-gritty of a matter, situation, or activity, they discuss the most important, basic parts of it or facts about it. the nitty gritty of everyday politics. the nitty-gritty the basic and practical facts of a subject or activity (Probably based on gritty)
the choicest or most essential or most vital part of some idea or experience; "the gist of the prosecutor's argument"; "the heart and soul of the Republican Party"; "the nub of the story"