What is the meaning of observance?

noun

• The act of observing; taking a patient look.
  • synonyms: observation, watching
• A formal event performed on a special occasion.
  • usage: "a ceremony commemorating Pearl Harbor"
  • synonyms: ceremony, ceremonial, ceremonial occasion
• The act of noticing or paying attention.
  • usage: "he escaped the notice of the police"
  • synonyms: notice, observation
• Conformity with law or custom or practice etc..
  • synonyms: honoring