Trauma is anything that overwhelms our ability to cope. We can consider overwhelm on a continuum from 'overwhelming stress' to 'PTSD' to 'developmental trauma'.
Post Traumatic Stress Disorder (PTSD) symptoms include involuntarily re-experiencing aspects of the traumatic event in a very vivid and distressing way, avoidance behaviour, hyperarousal, and, emotional numbing. 
‘Trauma occurs when an event creates an unresolved impact on an organism.’
'Dissociation is the essence of trauma.'
- Haines S (2016) Trauma Is Really Strange. London: Jessica Kingsley Publishers.
- NICE (2005) Post-traumatic stress disorder (PTSD): The management of PTSD in adults and children in primary and secondary. guidance.nice.org.uk/cg26 Accessed 2015-09-02
- Levine P (1997) Waking the Tiger – Healing Trauma. Berkeley, CA: North Atlantic Books.
- Van Der Kolk B (2014) The Body Keeps The Score: Brain, mind, and body in the healing of trauma. New York, Viking.