Emotional detachment, in psychology, can mean two different things.
Emotional detachment can be a positive behavior which allows a person to react calmly to highly emotional circumstances/ individuals. Emotional detachment in this sense is a decision to avoid engaging emotional connections, rather than an inability or difficulty in doing so, typically for personal, social, or other reasons. In this sense it can allow people to maintain boundaries, psychic integrity and avoid undesired impact by or upon others, related to emotional demands. As such it is a deliberate mental attitude which avoids engaging the emotions of others.
This detachment does not necessarily mean avoiding empathy; rather it allows the person space needed to rationally choose whether or not to be overwhelmed or manipulated by such feelings. Examples where this is used in a positive sense might include emotional boundary management, where a person avoids emotional levels of engagement related to people who are in some way emotionally overly demanding, such as difficult co-workers or relatives, or is adopted to aid the person in helping others such as a person who trains himself to ignore the "pleading" food requests of a dieting spouse, or indifference by parents towards a child's begging.
Emotional detachment can also be used to describe what is often considered "emotional numbing", "emotional blunting", i.e., dissociation, depersonalization or in its chronic form depersonalization disorder. This type of emotional numbing or blunting is a disconnection from emotion, it is frequently used as a coping/ survival skill during traumatic childhood events such as abuse or severe neglect. Over time and with much use, this can become second nature when dealing with day to day stressors.
Emotional detachment often arises from psychological trauma and is a component in many anxiety and stress disorders. The person, while physically present, moves elsewhere in the mind, and in a sense is "not entirely present", making them sometimes appear preoccupied.
Thus, such detachment is often not as outwardly obvious as other psychiatric symptoms; people with this problem often have emotional systems that are in overdrive. They may have a hard time being a loving family member. They may avoid activities, places, and people associated with any traumatic events they have experienced. The dissociation can also lead to lack of attention and, hence, to memory problems and in extreme cases, amnesia.