Wiktionary
n. A cause for an effect in a system that is not a constituent of that system, especially causes of personal health problems or death, such as poison, weapon wounds, or accident.
Wikipedia
In medicine, an external cause is a reason for the existence of a medical condition which can be associated with a specific object or acute process that was caused by something outside the body.
They are classified as "E codes" in ICD 9.
External Cause Of Injury Codes (E – Codes) are ICD-9-CM codes (link) or ICD – 10 codes (link) that are used to define the mechanism of death or injury, along with place of occurrence of the event. 1
E – codes are assigned on death certificates based on the manner of death. ICD – 10 codes in the range V01-X59 refer to unintentional injuries. Codes in the range X60-X84 refer to intentional self-harm. Codes in the range Y85-Y09 refer to assault, and codes in the range Y10-Y34 refer to events of undetermined intent. 2
E – codes are well collected on death certificate (link) data, but less so on hospital discharge data (link). Numerous initiatives have increased the percentage of records coded. (CDC, MMWR March 28, 2008 / Vol. 57 / No. RR-1) (link).