Open-source intelligence (OSINT): The practice of gathering, analyzing, and disseminating information from publicly available sources. It is used by law enforcement, intelligence agencies, and businesses to gather information about potential threats or targets. Examples include social media monitoring, web scraping, and public records research.

Open-source software (OSS): OSS is software with source code that anyone can inspect, modify, and enhance. It promotes collaboration and sharing since developers can access the source code to improve the software design or fix issues. OSS security depends on community involvement to identify and patch vulnerabilities promptly.

Open Storage: A type of data storage architecture that allows access to data without the need for proprietary software or hardware. It is commonly used in cloud computing environments to provide scalable and flexible storage solutions. Examples of open storage systems include the OpenStack Swift and Ceph projects.

Open System: A model of computing systems that provides some form of openness, such as open standards, interfaces, or source code. This openness promotes interoperability, portability, and user choice and allows users and developers to have significant influence over how the system operates. Open systems are often contrasted with closed systems, which are controlled by a single entity and where the inner workings of the system are not made available to users or developers.

Open System Authentication (OSA): A network security method for verifying user or device identity through a shared secret like a password or biometric data. It ensures that only authorized users can access sensitive resources, with examples including password-based logins, fingerprint scanners, and face recognition technology.

Open Systems Interconnect (OSI) Model: A conceptual structure that standardizes the functions of a communication system into seven distinct categories known as layers. These layers, from highest to lowest, include the application, presentation, session, transport, network, data link, and physical layers. Each layer provides specific services that contribute to overall network communication, fostering interoperability between various hardware and software systems.