In the analysis of personnel vulnerability and lethality, the taxonomy includes a number of words to describe the status of the target after an insult. The aim of this report is to describe the meaning of the most commonly used terminology and the basics of operational requirements-based casualty assessment. The basic concept of vulnerability and lethality (V/L) analysis is the operational capability of the target. That is true also for the assessment of human vulnerability although, humans in addition, can be assessed from a medical perspective. The methodology of operational requirements-based casualty assessment can be divided into three main steps: evaluation of the anatomic/physiological injury, relating the injury to degradation of elemental capabilities, and comparison of capability degradation and operational requirements. The task may be performed with full capability, with reduced capability or not at all. Depending on the situation the operational capability requirements are specified and if they are not fulfilled the target is defined as incapacitated. Typical results from an assessment are e.g. "100 % capability reduction in the assault situation" or "50 % capability reduction in the defence situation". An assessment can be performed a large number of times to result in a statistical probability of a specified outcome. The assessment may be to determine if the target is incapacitated according to the outcome "50 % capability reduction in the assault situation" with 80 % probability. The choice of outcome in the assessment depends on scenario and tactical situation. Personnel subjected to artillery fire may be incapacitated according to "50 % capability reduction in assault situation" whereas a soldier with an assault rifle in close quarter battle needs to be incapacitated according to a 100 % capability reduction in defence situation.