What is Puja?

The word "pūjā" is Sanskrit, and means reverence, honour, homage, adoration, and worship.
Puja, the loving offering of light, flowers, and water or food to the divine, is the essential ritual of Hinduism.

Puja is not mandatory in Hinduism. It may be a routine daily affair for some Hindus, periodic ritual for some, and rare for other Hindus. In some temples, various pujas may be performed daily at various times of the day; in other temples, it may be occasional.

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Indologist Jan Gonda has identified 16 steps (shodasha upachara) that are common in all varieties of puja:

1. Avahana (“invocation”). The deity is invited to the ceremony from the heart.
2. Asana. The deity is offered a seat.
3. Padya. The deity’s feet are symbolically washed.
4. Water is offered for washing the head and body
5. Arghya. Water is offered so the deity may wash its mouth.
6. Snana or abhisekha. Water is offered for symbolic bathing.
7. Vastra (“clothing”). Here a cloth may be wrapped around the image and ornaments affixed to it.
8. Upaveeda or Mangalsutra. Putting on the sacred thread.
9. Anulepana or gandha. Perfumes and ointments are applied to the image. Sandalwood paste or kumkum is applied.
10. Pushpa. Flowers are offered before the image, or garlands draped around its neck.
11. Dhupa. Incense is burned before the image.
12. Dipa or Aarti. A burning lamp is waved in front of the image.
13. Naivedya. Foods such as cooked rice, fruit, clarified butter, sugar, and betel leaf are offered.
14. Namaskara or pranama. The worshipper and family bow or prostrate themselves before the image to offer homage.
15. Parikrama or Pradakshina. Circumambulation around the deity.
16. Taking leave.

Sometimes additional steps are included:

1. Dhyana (“Meditation”). The deity is invoked in the heart of the devotee.
2. Acamanıya. Water is offered for sipping.
3. Aabaran. The deity is decorated with ornaments.
4. Chatram. Offering of umbrella.
5. Chamaram Offering of fan or fly-whisk (Chamara).
6. Visarjana or Udvasana. The deity is moved from the place.

There are variations in this puja method such as:

1. Pancha upachara pooja (puja with 5 steps).
2. Chatushasti upachara puja (puja with 64 steps).
   The structure of elaborate puja also varies significantly between temples, regions and occasions.

Source: (https://en.wikipedia.org/wiki/Puja_(Hinduism))