Though the nature of a project is temporary, they are not performed in isolation. They work in a controlled environment and affected by Enterprise Environmental Factors (EEF) and Organizational Process Assets (OPA).
The Project Management Institute terms them as influences. Enterprise environmental factors can be internal or external, while organizational process assets are always internal to an organization.
Enterprise environmental factors and organizational process assets are widely discussed in the PMBOK Guide and are inputs of almost all processes. You must have a thorough understanding of these terms.
Although the concepts are straightforward, many PMP aspirants fail to understand them and often make mistakes on the exam.