When I talk about trauma in therapy, I am referring to how the nervous system responds as opposed to a specific event that occurred. Trauma impacts people when they perceive they or a loved one is in danger. Danger may or may not actually be present, but the nervous system is not always that logical. In addition to traumatic events, the nervous system may respond to chronic stress, dramatic change, or prolonged chaos as if trauma were present.
Long after the situations which lead us to where we are now have passed, our body and nervous system may continue to function as if it is still ongoing. Basically, our body remains on guard for danger or attempts to sustain fight, flight, or freeze mode. People respond to trauma in many ways, so they may be impacted by trauma even if they do not meet diagnostic criteria for PTSD (Post Traumatic Stress Disorder). Therapy can help restore the nervous system for real healing, and it can build resilience in our nervous system, emotions, and life functioning.
Here are some resources to learn more about trauma, in addition to therapy with a specially trained counseling professional: http://www.traumahealing.com/somatic-experiencing/bookstore_all.html