The concept of trusting software is applicable to any system, regardless of the level of security implemented; the process of trusting software will lead to a more secure installation.
Trust is the belief that a system element upholds the security policy of an operating system. If this belief is founded on blind faith, disasters are likely to happen, so it makes sense to assign trust only when a system element has been shown to deserve that trust.
For user-level software, this means making sure that a command or library routine works as advertised, and prevents unauthorized users from circumventing access controls or mechanisms that protect sensitive system operations. In this topic, trust refers not to blind faith, but to confirmed trustworthiness.