compartment: a set of programs and data to be partitioned or separated, where users are given explicit access to specific component of a system. A compartment represents a grouping, such as a work group, department, project, or topic. Compartments make it possible to implement a need-to-know-basis security policy.

integrity: the level of trust which can be placed on data. As the integrity of the data is elevated, so does the ability to trust that data.

level: the increased or decreased setting of a security attribute. As the level increases, its security is considered to elevate as well.

label: a security attribute which can be applied to files, directories, or other items in the system. It could be considered a confidentiality stamp. When a label is placed on a file, it describes the security properties of that file and will only permit access by files, users, and resources with a similar security setting. The meaning and interpretation of label values depends on the policy configuration. Some policies treat a label as representing the integrity or secrecy of an object while other policies might use labels to hold rules for access.

multilabel: this property is a file system option which can be set in single-user mode using tunefs(8), during boot using fstab(5), or during the creation of a new file system. This option permits an administrator to apply different MAC labels on different objects. This option only applies to security policy modules which support labeling.

single label: a policy where the entire file system uses one label to enforce access control over the flow of data. Whenever multilabel is not set, all files will conform to the same label setting.

object: an entity through which information flows under the direction of a subject. This includes directories, files, fields, screens, keyboards, memory, magnetic storage, printers or any other data storage or moving device. An object is a data container or a system resource. Access to an object effectively means access to its data.

subject: any active entity that causes information to flow between objects such as a user, user process, or system process. On FreeBSD, this is almost always a thread acting in a process on behalf of a user.

policy: a collection of rules which defines how objectives are to be achieved. A policy usually documents how certain items are to be handled. This chapter considers a policy to be a collection of rules which controls the flow of data and information and defines who has access to that data and information.

high-watermark: this type of policy permits the raising of security levels for the purpose of accessing higher level information. In most cases, the original level is restored after the process is complete. Currently, the FreeBSD MAC framework does not include this type of policy.

low-watermark: this type of policy permits lowering security levels for the purpose of accessing information which is less secure. In most cases, the original security level of the user is restored after the process is complete. The only security policy module in FreeBSD to use this is mac_lomac(4).

sensitivity: usually used when discussing Multilevel Security (MLS). A sensitivity level describes how important or secret the data should be. As the sensitivity level increases, so does the importance of the secrecy, or confidentiality, of the data.