Adolescence – transitional stage between childhood and adulthood (11–20 years of age).

Desensitization – diminishing emotional and physiological reaction to unpleasant stimuli through frequent exposure to these stimuli.

Empathy – adopting and understanding emotional point of view of another person.

Impulsiveness – limited control of emotions as well as thoughts and behaviours they entail.

Narcissism – feature of a narcissistic personality associated with a shaky and unstable self-esteem, unrealistic perception of oneself and one’s own capabilities as well as excessive sensitivity to criticism.

Ostracism – exclusion of a person from their group.

Transference and countertransference – redirection of a patients feelings toward a psychotherapist and psychotherapist’s feelings toward a patient.

Self-esteem – affective attitude towards oneself (manner of assessing oneself).

Autism spectrum disorders – or autism spectrum, range of neurodevelopmental conditions characterized by permanent, severe difficulties in maintaining relations and social communication as well as limited, repetitive and nonflexible patterns of behaviours and interests.

Suicidal tendencies – suicidal thoughts and actions.

Major depressive disorder – group of mental disorders with a clinical picture dominated by low mood, sadness, feeling of guilt and unworthiness. The disorders are characterized by diversified level of intensity.

Anxiety disorder – mental disorder with a clinical picture dominated by anxiety. It is accompanied by strong physiological reactions. The disorders are characterized by diversified level of intensity.

Self-destructive behaviours – self-injuring and self-mutilation, activities directing the aggression at oneself in order to ease the emotional tension.