S: This stands for Position (for example, HR Manager, Marketing Director, and so on)
P: This stands for Person
O: This stands for Organizational unit (also known as Org unit; it represents the department in a company)
C: This stands for Job (for example, manager, director, and so on)
K: This stands for Cost Center
Note that both K and P are external object types. The K object type, Cost Center, is maintained in the FI/CO module, and the P object type, Person, is maintained in the PA submodule. When we say external, it is simply not created in the OM submodule.
SAP has delivered multiple interfaces to design an organizational structure, and we will understand each of them separately.