Generally it is a specific traumatic event that a person experiences or witnesses. For me there was an inciting event followed by additional compounding events, but they were all specific to that initial trauma. PTSD events could be something like a rape, a war event, a natural disaster, witnessing a death, etc. CPTSD is generally considered the result of chronic trauma so for instance the result on long-term repeated abuse.

The DSM does not use CPTSD as a diagnosis so if you are in the USA which functions under the DSM, officially they have to use PTSD as the diagnostic code.