What is the meaning of marrow?

noun

• The fatty network of connective tissue that fills the cavities of bones.
  • synonyms: bone marrow
• Any of various squash plants grown for their elongated fruit with smooth dark green skin and whitish flesh.
  • synonyms: marrow squash, vegetable marrow
• Very tender and very nutritious tissue from marrowbones.
  • synonyms: bone marrow
• Large elongated squash with creamy to deep green skins.
  • synonyms: vegetable marrow
• The choicest or most essential or most vital part of some idea or experience.
  • usage: "the gist of the prosecutor's argument"; "the heart and soul of the Republican Party"; "the nub of the story"
  • synonyms: kernel, substance, core, center, centre, essence, gist, heart, heart and soul, inwardness, meat, nub, pith, sum, nitty-gritty