Der Derian defines it this way:  “Securitization is the political construction of an issue that is not objectively essential to national survival, but has been portrayed as such by the government in power. Once an issue is labeled as a threat to national security, the issue takes priority above all other political issues, and governments can violate laws that must otherwise be obeyed. Through the process of securitization the legitimacy and strength of the acting powers are reinforced – as is the authority to create policy.” 

How does this concept relate to our discussion of different ways of defining the state’s obligation to provide security?  Der Derian seems to assume there is clear distinction that can be made between issues that are “objectively  essential to national survival” and those that are not.  So it seems to be  a concept for distinguishing between legitimate and illegimate uses of the term “security.”