Psychologists play powerful roles in people's lives. However, they should never abuse their power. An abuse of power would be a psychologist initiating a romantic relationship with a client. In fact, it is unethical for a psychologist to even be friends with their clients. The reason is that a psychologist is considered a type of doctor of the mind. It would be like a gynecologist looking up and asking their patient on a date. Awkward.
It's called psychological abuse when a psychologist creates a power imbalance with their clients. As you may be able to glean from the term, psychological abuse is something you want to stay away from. Patients tend not to like having the trust they placed in their psychologist taken advantage of after they've given them access to their brains, and exposed their full frontal lobe.