In general, trauma is a psychological, emotional and physical response to a deeply stressful and disturbing experience.
As a consequence of a traumatic event, people can develop Post-Traumatic Stress Disorder (PTSD) which is an anxiety disorder that causes the person to relive the traumatic event through flashbacks and nightmares, have sleeping problems, feel isolated, irritable and guilty.
If the traumatic experience happens repeatedly overtime (for instance repeated childhood abuse), the person might experience Complex PTSD.
EMDR is recommended to treat PTSD. EMDR can also be used in Complex PTSD, in combination with other approaches like Sensorimotor Therapy to restore a connection with our bodies and address the somatic components of the trauma we experienced.