Organizational unit
In systems made up of people, the constructive parts/modules are primarily the people themselves, with their audio, visual, tactile, and other interfaces.
It should be noted that the functions of people are not even attempted to be discussed, nor the meaning and content of information or changes in the environment that come to people and go from them through the interfaces of the human body. This is a modular/product-oriented approach, that is, considering "how to do it", how to put together a system of people as they are.
People have a special type of relationships that indicate the possibility of disposing of various means of production, or even other people: we are talking about ownership rights, the authority to give orders to other people, the authority to accept work from other people, the authority to exchange goods or services (including the case when we talk about a "universal item" - money). To obtain the required external behavior from a person, you need to have the corresponding authority recognized by them. People who have agreed on authorities regarding each other and their means of production, on mutual responsibilities, are called organized, and a system of such people is called an enterprise/organizational unit that provides services to other enterprises/organizational divisions. The term "organization" is most often used in relation to the top of the modular breakdown of a system of people and means of production (enterprise/company/corporation or in the case of governmental and nonprofit organizations, other names are used - authorities, agencies, institutions, associations, funds, etc.), and intermediate levels are called "organizational divisions." The minimum organizational unit is thus one person, but since people have long ceased to alter the physical world with their bare hands and do not use bare channels of perception, this is one person with their tools, which they are authorized to dispose of. Considering that people in an organization must collaborate, they are called employees. The minimum organizational unit is one employee with the equipment assigned to them.
Further, these minimum organizational units/employees/people are combined based on their recognized authorities into organizational units of the next level, and so on - until the organizational unit of the highest level turns out to be the organization as a whole (enterprise or institution, or association, or fund, etc.). Are there systemic levels above the organization level? Yes: production cooperatives, business ecosystems, movements, and so on. It's just that at these systemic levels there is no organization, authorities are not distributed, so joint actions to coordinate the use of resources are based on direct agreements to create "extended enterprises" (extended enterprises, organizations consisting of organizations that have agreed to perform some common tasks). For example, a nuclear power plant is constructed by an extended enterprise - hundreds and thousands of contractor enterprises, not just one construction and installation organization ("construction" is construction plus installation of complex equipment). The construction and installation organization of the nuclear power plant has contracts with its subcontractors, these contracts define who is responsible for what in the construction of the nuclear power plant: not at the level of individual people, but immediately at the level of organizations.
The term "organizational unit" is better than the term "department" because in the modular structure of an organization, temporary organized groups of people and their means of production are usually not shown: project groups (projects are temporary, after all!), as well as various councils, committees, clubs, commissions, and so on. But when you are told that "to launch a new project, a decision of the scientific and technical council is required," you need to somehow take this into account in the system description. But the scientific and technical council is not a department! If we generalize the concept for all entities that are empowered to make decisions and perform actions related to these decisions at units and such "collegial bodies" that meet at separate sessions (and even those often held through email exchanges or chat discussions), we will indeed get an "organizational unit": a part that makes up the organization.
The entire modular/organizational structure and interfaces between organizational units are discussed not in connection with how to improve something in the organizational system (the organization/organizational unit's operating time), but specifically in connection with "how to organize" - who will execute whose orders, what and when will be purchased as means of production, and who will manage them. The subject of modular/organizational discussion in organizations/organizational units is organization (achieving a state of organization when the authorities of all employees are understood).
The services of organizational units (both permanent units and temporary collegial groups - project teams, working groups, departments, councils, committees, and so on) provided by them at their organizational interfaces, the discussion of interfaces and interface modules/channels (email, issue tracker, cash register, conveyor belt, etc.) for interacting with them, are a typical subject of discussion in organizations. In good organizations, these services are tried to be standardized (regulated: brought in line with the standards of the enterprise level), made into some kind of organizational platform with a published interface.
An organization/enterprise is literally composed, assembled, made up of its organizational units, these are constructive, not functional parts of the enterprise/organization. From discussing the organizational diagram, you can't tell how the company works, what functions the organizational units of the company perform.
Naming organizational units in this consideration of "how it's done, what it's made of" often reflects more than it doesn't. In names, the most general ideas about the service provided are reflected, regardless of the purpose/function of that service. Workshop No. 5, Ward No. 6 - simple numbers in names, which do not indicate functions, are typical indicators of a constructive view. The most general words without specifying the subject area (like "database" and "server" in information technology) are a similar feature ("engineering", "legal department", scientific and technical council, project group).
Organizational units' constructive elements can perform multiple, even unexpected, functions. On the other hand, if "the department moves to another building," this describes the connection of the constructive and placement aspects of the department. "The department will perform new practices/types of activities" - this is a discussion of the link between the functional and constructive aspects of the department.