In a democratic society, imprisonment without trial is considered a violation of human rights and is generally prohibited. However, there may be certain exceptional circumstances where a government may impose imprisonment without trial under certain categories of people. These circumstances may include national security concerns, public safety, and emergency situations. In India, there are several laws that allow for imprisonment without trial in certain situations.

The categories of people who can be imprisoned without trial in India are as follows:

1. Enemy aliens: Enemy aliens are individuals who are citizens of a country with which India is at war. The government may imprison enemy aliens without trial for the duration of the war or until they are repatriated to their home country.
2. Preventive detention: Preventive detention is a measure taken by the government to detain individuals who are deemed to be a threat to national security or public safety. The government can detain such individuals without trial for a period of up to two years under the provisions of the Conservation of Foreign Exchange and Prevention of Smuggling Activities Act, 1974.
3. Maintenance of Internal Security Act (MISA): The MISA allows for the detention of individuals who are deemed to be a threat to the maintenance of internal security in the country. The government can detain such individuals without trial for a period of up to one year.
4. Armed Forces (Special Powers) Act (AFSPA): The AFSPA allows for the detention of individuals who are suspected of being involved in terrorist activities or activities that are detrimental to national security. The government can detain such individuals without trial for a period of up to one year.
5. National Security Act (NSA): The NSA allows for the detention of individuals who are suspected of being a threat to national security. The government can detain such individuals without trial for a period of up to one year.

It is important to note that imprisonment without trial is a serious violation of human rights and should only be used in exceptional circumstances. The government must ensure that the individuals who are detained are given a fair hearing and are allowed to defend themselves against any charges that are made against them. The use of imprisonment without trial should always be subject to strict legal oversight to prevent abuse and ensure that the rights of the individual are protected.