What is the meaning of kernel?

noun

• The inner and usually edible part of a seed or grain or nut or fruit stone.
  • usage: "black walnut kernels are difficult to get out of the shell"
  • synonyms: meat
• A single whole grain of a cereal.
  • usage: "a kernel of corn"
• 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: substance, core, center, centre, essence, gist, heart, heart and soul, inwardness, marrow, meat, nub, pith, sum, nitty-gritty