“Pachakhan” (पच्चक्खाण / पच्चखान) means a vow or promise taken before doing any tapa (fast / food‑restraint). Different pachakhans are based mainly on time of eating, number of meals, and night‑eating rule.

Below are the main kinds commonly practiced (names may differ a little by region, but idea is same):

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1. According to time after sunrise

1. Navkarsi Pachakhan

- Do not eat or drink anything till 48 minutes after sunrise. - After that, sit in one place, do Navkar, and then take food or water.

1. Porsi Pachakhan

- Do not eat or drink anything till one prahar (¼ of daytime) after sunrise (roughly 3 hours after sunrise). - Then sit, do Navkar and take food/water.

1. Sadh‑Porsi Pachakhan (Sāḍhporsi)

- No food or drink till 1½ prahar after sunrise (about 4½ hours after sunrise).

1. Purimaddh Pachakhan

- Eat only till mid‑day (before the middle of the day).

1. Avaddh Pachakhan

- Eat only till a fixed earlier time (before a decided limit of the day). - After that time, no food or drink.

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2. According to number / type of meals

1. Upvās Pachakhan

- No food the whole day. - Only boiled water, and that too only in fixed time (often from Porsi to sunset).

1. Tivihaar Upvās Pachakhan

- Upvās with very strict rules: - No food all day. - Only boiled water in limited timings, plus some extra restraints (no going out unnecessarily, carefulness, etc.).

1. Ayambil Pachakhan

- One meal in the day, very plain (ras‑tyag) – no ghee, oil, milk, curd, sugar, fruits, spices, etc. - Only boiled, tasteless type food in one sitting.

1. Ekasana (Ekāsan) Pachakhan

- Eat only once in the whole day, in one sitting.

1. Biyasana (Biyāsan) Pachakhan

- Eat twice in the day (two sittings only).

1. Nivi Pachakhan

- Very limited, fixed quantity / type of food decided in advance.

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3. According to night‑eating rule

1. Pānhār (Panhar) Pachakhan

- No food or drink after sunset till next sunrise. - Usually taken after doing Upvās, Ayambil, Ekasan, Biyasan, etc.

1. Chovihār / Tivihār (depending on tradition)

- Broader rules on not eating in the night or limiting water timings. - Details vary, but essence is: avoid food (and often water) at night.

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4. Special / personal pachakhan

• Dharna‑Abhigrah Pachakhan

- A personal resolve: e.g. “For these many days I will daily do Navkarsi + Panhar,” or “for 8 days I will do Ayambil,” etc. - This is decided in front of a Guru / elder / in front of Dev‑Guru‑Dharma.

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In simple words:

• Pachakhan = promise to Bhagwan that,

“Today I will eat / drink only in this way, at this time, with these limits.”

• It helps in saiyam (self‑control) and nirjarā (shedding of karma), and builds inner discipline.

You can read a simple explanation of Pachakhan here