observance

Short definition from Wiktionary

Noun

1. 1
   The practice of complying with a law, custom, command or rule.
2. 2
   The custom of celebrating a holiday or similar occasion.
3. 3
   Observation or the act of watching.
4. 4
   A rule governing a religious order, especially in the Roman Catholic church.
5. 5
   That which is to be observed.
6. 6
   Reverence; homage.