There are many mental illnesses where you may hallucinate. They
include schizophrenia, schizoaffective disorder, schizophreniform
disorder, shared psychotic disorder, brief psychotic disorder,
substance-induced psychotic disorder, bipolar disorder, major
depression with psychotic features, delirium, and dementia.
However, when someone talks about a mental illness in which you
"hear things" or "see things" it will usually be schizophrenia.