Atrocious is a form of adjective.
The meaning of atrocious is 'extremely cruel, evil'. The meaning of atrocious is also used to refer something as shameful or shocking.
'Very bad or unpleasant' is another meaning of atrocious.
The following sentences explain the meaning of atrocious more clearly.
1. You have done an atrocious crime.
2. Private companies are known for their atrocious working conditions.
3. It was an atrocious meal !