Vulnerability

Vulnerability is the susceptibility to physical or emotional injury or attack. It also means to have one's guard down, open to censure or criticism; assailable. Vulnerability refers to a person's state of being liable to succumb, as to persuasion or temptation (see Thywissen 2006 for a comparison of vulnerability definitions).

Common application: In relation to hazards and disasters, vulnerability is a concept that links the relationship that people have with their environment to social forces and institutions and the cultural values that sustain and contest them. “The concept of vulnerability expresses the multidimensionality of disasters by focusing attention on the totality of relationships in a given social situation which constitute a condition that, in combination with environmental forces, produces a disaster” (Bankoff et al. 2004: 11).

It's also the extent to which changes could harm a system.

Emerging research: Vulnerability research covers a complex, multidisciplinary field including development and poverty studies, public health, climate studies, security studies, engineering, geography, political ecology, and disaster and risk management. This research is of particular importance and interest for organizations trying to reduce vulnerability--especially as related to poverty and other Millennium Development Goals. Many institutions are conducting interdisciplinary research on vulnerability. A forum of that brings many of the current researchers on vulnerability together is the Expert Working Group (EWG).1 Researchers are currently working to refine definitions of “vulnerability”, measurement and assessment methods, and effective communication of research to decision makers (Birkmann et al. 2006).

Major research questions: Within the body of literature related to vulnerability, major research streams include questions of methodology, such as: measuring and assessing vulnerability, including finding appropriate indicators for various aspects of vulnerability, up- and downscaling methods, and participatory methods (Villagran 2006).

A sub-category of vulnerability research is social vulnerability, where increasingly researchers are addressing some of the problems of complex human interactions, vulnerability of specific groups of people, and shocks like natural hazards, climate change, and other kinds of disruptions. The importance of the issue is indicated by the establishment of endowed chairs at university departments to examine social vulnerability.

Military Vulnerability
In military circles Vulnerability is a subset of Survivability (the others being Susceptibility and Recoverability. Vulnerability is defined in various ways depending on the nation and service arm concerned, but in general it refers to the near-instantaneous effects of a weapon attack. In some definitions Recoverability (damage control, firefighting, restoration of capability) is included in Vulnerability.

A discussion of warship vulnerability can be found here

Invulnerability
The term Invulnerability is a common feature found in video games. It makes the player impervious to pain, damage or loss of health. It can be found in the form of "powerups" or cheats.