Security has to be compared and contrasted with other related concepts: Safety, continuity, reliability. The key difference between security and reliability is that security must take into account the actions of people attempting to cause destruction.
For example, the fear of earthquakes has been reported to be more common than the fear of slipping on the bathroom floor although the latter kills many more people than the former.
The presence of security protections may be taken for security itself. For example, two computer security programs could be interfering with each other and even cancelling each other's effect, while the owner believes s/he is getting double the protection.
Security Theatre is a critique's term for deployment of measures primarily aimed at raising subjective security in a population without a genuine or commensurate concern for the effects of that measure on--and possibly decreasing--objective security. For example, some consider the screening of airline passengers based on static databases to have been Security Theater and Computer Assisted Passenger Prescreening System to have created a decrease in objective security.