Answer:
Ritual.
Explanation:
As the exercise exemplifies, a ritual is a series of activities that could include from a dance, a song, an omen, words, totems or objects, etc., performed in a particular plance, date, background, etc. In the example, the ritual is to decorate their house based on the themes of various horror films. This being an annual practice, on a particular date, bringing out a series of actions from the family members is their ritual.
