What is the meaning of rudiments?

noun

• The elementary stages of any subject (usually plural. )
  • usage: "he mastered only the rudiments of geometry"
  • synonyms: rudiment, first rudiment, first principle, alphabet, ABC, ABC's, ABCs
• The remains of a body part that was functional at an earlier stage of life.
  • usage: "Meckel's diverticulum is the rudiment of the embryonic yolk sac"
  • synonyms: rudiment
• A statement of fundamental facts or principles.
  • synonyms: basics