A bizarre delusion is an impossible belief that cannot possibly be true in reality. Delusions, a common symptom in schizophrenia, are false beliefs that the sufferer believes to be true. Non-bizarre delusions are false beliefs that could be true in reality. For example, a non-bizarre delusion would be an individual who believes their neighbor is a spy who has them under constant surveillance. This is a non-bizarre delusion because although it is a false belief it could be true. Although it is not impossible the neighbor could be a spy and this is a situation that could happen. Bizarre delusions are impossible and could never happen in reality.
For example, a bizarre delusion would be an individual who believes their dog works at a grocery store when they leave the house. Another example of a bizarre delusion is the Cotard delusion - sufferers believe they are dead and are a walking corpse.