Here are some examples of how "psych" is used in English:
* Psychology: the scientific study of the mind and behavior
* Psychiatry: the branch of medicine that deals with the diagnosis, treatment, and prevention of mental illnesses
* Psychopath: a person suffering from a chronic mental disorder with abnormal or violent social behavior
* Psychotropic: affecting the mind
* Psychedelic: producing hallucinations
* Psychic: relating to or having a special sensitivity to nonphysical forces
So, in essence, "psych" refers to the inner world of the mind, thoughts, feelings, and behavior.