Preventive detention refers to the act of detaining an individual without carrying out any interrogation or formal charges against them. It is done as a precautionary measure to prevent potential threats to public safety, maintenance of public order, or national security. This means that a person can be detained without any specific crime being committed or proven against them.

Option 1, detention for interrogation, suggests that the purpose of preventive detention is for gathering information through questioning. However, this is not accurate as preventive detention does not involve any interrogation.

Option 2, detention after interrogation, implies that preventive detention is carried out after an interrogation has taken place. This is incorrect as preventive detention does not require any prior questioning or interrogation.

Option 4, detention for cognisable offence, states that preventive detention is for detaining individuals who have committed a cognisable offense. However, preventive detention is not contingent upon any offense being committed or even proven.

Therefore, option 3, detention without interrogation, is the correct and accurate description of preventive detention.