In Jainism, "Kathor" refers to certain types of vegetables that are considered hard or underground and are typically avoided, especially by stricter adherents and during specific periods like Paryushan or on certain tithis (dates in the lunar calendar). The term "Kathor" (कठोर) literally means "hard" or "firm." In the context of vegetables, it generally refers to:

• Underground vegetables (root vegetables): These include potatoes, onions, garlic, carrots, radishes, beets, sweet potatoes, yams, and similar items.
• Bulbs and tubers: Anything that grows underground and is harvested by uprooting the plant, which is believed to cause harm to many life forms (as per the principle of non-violence or ahimsa in Jainism).

Jains avoid "Kathor" vegetables because harvesting them kills the entire plant and also disturbs countless tiny organisms living in the soil, thereby increasing violence (himsa). Instead, Jains are encouraged to consume above-ground vegetables and fruits that can be harvested without destroying the plant.

In summary, "Kathor" in Jain dietary practice refers to hard, underground vegetables and tubers that are generally avoided to minimize violence and uphold the principle of ahimsa.