Undesirables are people who a particular government considers to be dangerous or a threat to society, and therefore wants to get rid of. The Home Office is usually quick to deport undesirables. something or someone that is undesirable is not welcome or wanted because they may affect a situation or person in a bad way undesirable effects/consequences etc. someone who is considered to be immoral, criminal, or socially unacceptable
If you describe something or someone as undesirable, you think they will have harmful effects. Inflation is considered to be undesirable because of its adverse effects on income distribution A large group of undesirable strangers crashed her party