POSITIVE: In the field of psychology, positive does mean happy or upbeat, like inspirational quotes. Instead, it means that something is being added. So, the term “positive punishment” may sound like an oxymoron, but it in fact means that someone is punishing by adding something to the mix (e.g., spanking, shocks). This is also used in reference to symptoms of mental disorders. People with schizophrenia experience hallucinations. This would be a positive symptom of schizophrenia; not because it is a good thing, but because it is something more than what healthy people experience.
NEGATIVE: Negative means the opposite of positive. It does not necessarily mean bad; it means that something is being taken away. So, “negative reinforcement” makes since as it involves the removal of some factor that causes pain or is unpleasant in some way (e.g., a child that ceases screaming after a parent gives them candy). A negative symptom of schizophrenia is anhedonia, a reduction in the experience of pleasure. When experiencing this symptom, a normal part of human life (happiness, pleasure) is removed and is therefore negative.