nitty-gritty

Noun

• 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
    

Related words

• Synonyms: 
  kernel , substance , core , center , centre , essence , gist , heart , heart and soul , inwardness