Step 1: Understanding the Concept:
A delusion is a fixed, false belief that is resistant to reason or confrontation with actual fact. The question asks for the term that describes a mental disorder characterized by delusions.
Step 2: Detailed Explanation:
(A) Paranoia: This term is often used to describe a specific type of delusion involving intense and irrational suspicion or mistrust of others (persecutory delusions). It describes a condition characterized by delusions.
(B) Delusional disorder: This is a formal psychiatric diagnosis (from the DSM-5) for a condition where the primary symptom is the presence of one or more delusions for at least a month, without other schizophrenic symptoms.
(C) Paranoid state: This is a more general, descriptive term for a mental condition characterized by paranoid delusions.
(D) All of these: Since paranoia is a state involving delusions, delusional disorder is the formal name for it, and paranoid state is a descriptive term for it, all three options refer to a mental disorder where a person suffers from delusions.
Step 3: Final Answer:
All the terms provided describe a mental disorder or state in which delusions are a primary feature. Therefore, "All of these" is the correct and most comprehensive answer.