Expand Threat Actor description

**User Account:** An identity created in an operating system with associated access controls and privileges. Users may have multiple user accounts and user accounts may have multiple users.

**Threat Agent:** An entity that can adversely act on an asset.

**Threat Actor:** An entity that can adversely affect the system through malicious or unauthorized activities.

**Application:** Software that runs on a platform and performs tasks on behalf of the user or owner of the platform, as well as its supporting documentation.