This glossary defines the eighteen most important terms in modern trauma therapy, from somatic experiencing to the Window of Tolerance to complex PTSD. Each entry explains what the term means, who developed it, and why it matters for survivors trying to make sense of their experience and find the right help. The trauma field has exploded over the past thirty years, driven by work from Bessel van der Kolk at the Trauma Center, Peter Levine at the Foundation for Human Enrichment, Judith Herman at Harvard, and Stephen Porges at Indiana University. If you are reading this as a survivor, therapist, or loved one, this vocabulary will help you understand what your body is doing, what treatments exist, and how to talk about your experience without feeling broken. Importantly, trauma is not only event-based: Gabor Mate and others emphasize that chronic neglect, emotional invalidation, and relational injuries can produce the same nervous system dysregulation as acute trauma. The terms below cut across modalities (EMDR, Internal Family Systems, somatic experiencing) because survivors often benefit from understanding the shared vocabulary. Complex PTSD is now in the ICD-11 (the World Health Organization diagnostic manual) as a formal diagnosis. This glossary uses plain language throughout. Return to it whenever a therapist uses a term you do not recognize.

1. What Is Somatic Experiencing?

Somatic experiencing (SE) is a body-based trauma therapy developed by Peter Levine in the 1970s. It works by tracking bodily sensations to help the nervous system complete thwarted fight or flight responses. Levine observed that wild animals rarely develop trauma because they discharge survival energy; humans override this. SE is slow, gentle, and nonverbal. It matters because it bypasses talking when talking retraumatizes. Citation: Levine, Waking the Tiger (1997).

2. What Is EMDR?

EMDR (Eye Movement Desensitization and Reprocessing) was developed by Francine Shapiro in 1987. It uses bilateral stimulation (eye movements, tapping, or tones) while the client holds a traumatic memory in mind. Meta-analyses (Chen et al. 2014) show it matches cognitive behavioral therapy for PTSD with fewer sessions. The WHO endorses it as a first-line PTSD treatment. Citation: Shapiro, Journal of Traumatic Stress (1989).

3. What Is Polyvagal Theory?

Polyvagal theory was introduced by Stephen Porges in 1994. It proposes that the vagus nerve has two branches: a ventral branch supporting social engagement and a dorsal branch driving shutdown. Trauma disrupts the ventral branch, leaving people stuck in fight, flight, or freeze. It matters because it gave clinicians a map of the nervous system. Citation: Porges, The Polyvagal Theory (2011).

4. What Is the Window of Tolerance?

The Window of Tolerance is a term coined by Dan Siegel (1999) for the zone of arousal in which a person can function well, neither overwhelmed nor shut down. Trauma narrows the window. Above it is hyperarousal; below it is hypoarousal. Therapy expands the window. It matters because it gives survivors language for noticing when they leave the zone. Citation: Siegel, The Developing Mind (1999).

5. What Are Fight, Flight, Freeze, and Fawn?

Fight, flight, and freeze are the classic trauma responses identified by Walter Cannon (1929) and expanded by Stephen Porges. Pete Walker added fawn in 2003 to describe the trauma response of appeasing to avoid harm. Fawn is common in childhood trauma survivors and often looks like people-pleasing. Citation: Walker, Complex PTSD From Surviving to Thriving (2013).

6. What Is Dissociation?

Dissociation is a protective splitting of awareness, memory, identity, or perception during or after overwhelming experience. It ranges from mild spacing out to dissociative identity disorder. Onno van der Hart described structural dissociation in The Haunted Self (2006). It matters because dissociation often gets mistaken for laziness, distraction, or disinterest. Citation: van der Hart, Nijenhuis and Steele (2006).

7. What Is Hyperarousal?

Hyperarousal is the state of being overactivated: racing heart, hypervigilance, startle response, insomnia, irritability. It is the sympathetic nervous system stuck on. PTSD criteria include it. In polyvagal terms, hyperarousal is sympathetic activation without access to social engagement. It matters because it is often confused with anxiety disorder when the root is trauma.

8. What Is Hypoarousal?

Hypoarousal is the state of being shut down: numbness, exhaustion, emptiness, disconnection, brain fog. It is dorsal vagal activation, the freeze response. Survivors often describe it as depression, but it has a different physiological signature. It matters because many survivors alternate between hyper and hypo without ever touching the Window of Tolerance.

9. What Are Triggers?

A trigger is any stimulus (sight, sound, smell, word, situation) that activates a trauma response by reminding the nervous system of the original event. Triggers are not always consciously recognized. Van der Kolk's neuroimaging showed that triggered survivors show Broca's area deactivation, making language hard. It matters because triggers are involuntary, not choices. Citation: van der Kolk, The Body Keeps the Score (2014).

10. What Are Flashbacks?

Flashbacks are involuntary intrusive re-experiences of trauma, ranging from full sensory re-immersion to emotional flashbacks (Pete Walker's term) where only the feeling returns without visual memory. Emotional flashbacks are central to complex PTSD. It matters because survivors often do not know emotional flashbacks are flashbacks at all.

11. What Is Trauma Bonding?

Trauma bonding was named by Patrick Carnes in 1997 for the attachment that forms between an abused person and their abuser through cycles of cruelty and intermittent reinforcement. It is biochemical, not stupidity. Stockholm syndrome is one example. It matters because survivors blame themselves for loving someone who hurt them. Citation: Carnes, The Betrayal Bond (1997).

12. What Is Complex PTSD?

Complex PTSD (C-PTSD) was proposed by Judith Herman in 1992 for the syndrome resulting from prolonged, repeated trauma (childhood abuse, captivity, domestic violence). It adds emotional dysregulation, negative self-concept, and relational difficulties to classic PTSD. The ICD-11 added it as a formal diagnosis in 2018. Citation: Herman, Trauma and Recovery (1992).

13. What Is Internal Family Systems?

Internal Family Systems (IFS) was developed by Richard Schwartz in the 1980s. It proposes the mind contains multiple parts (protectors, exiles, managers) around a core Self that is naturally compassionate. Therapy involves befriending parts rather than fighting them. A 2021 RCT by Hodgdon et al. showed IFS effective for PTSD. Citation: Schwartz, Internal Family Systems Therapy (1995).

14. What Is Parts Work?

Parts work is any therapy that treats the psyche as having distinct inner parts (IFS, ego state therapy, voice dialogue). It matters because survivors often feel at war with themselves, and parts work gives them a way to stop the war by listening to each side. It is particularly useful for dissociative experiences.

15. Who Is Bessel van der Kolk?

Bessel van der Kolk is a Dutch psychiatrist whose 2014 book The Body Keeps the Score brought trauma science to the mainstream. He founded the Trauma Center at Justice Resource Institute and has published over 150 peer-reviewed papers on PTSD neuroimaging. His research showed trauma lives in the body, not just the mind. Citation: van der Kolk, The Body Keeps the Score (2014).

16. Who Is Peter Levine?

Peter Levine is the psychologist who developed somatic experiencing after observing that animals discharge survival energy through trembling while humans freeze it in the body. His PhD work and decades of clinical practice produced a nonverbal trauma therapy used worldwide. Citation: Levine, Waking the Tiger (1997) and In an Unspoken Voice (2010).

17. Who Is Judith Herman?

Judith Herman is a Harvard psychiatrist who proposed complex PTSD in 1992 and whose book Trauma and Recovery is considered the foundational text of modern trauma therapy. She described the three stages of recovery: safety, remembrance and mourning, and reconnection. Citation: Herman, Trauma and Recovery (1992).

18. What Is Body Memory?

Body memory is the concept that the body stores trauma outside conscious narrative memory, expressed through tension, posture, chronic pain, and somatic symptoms. Van der Kolk's neuroimaging supports it: trauma often bypasses the hippocampus. It matters because it explains why talking alone may not heal, and why bodywork can access what words cannot.