"External sources" refer to information, data, or resources that come from outside of a specific context or system. It can be anything obtained from outside of an organization, person, or environment. Full definition
But the behavior of systems that are far from equilibrium, which are connected to the outside environment and strongly driven by external sources of energy, could not be predicted. (scientificamerican.com)
Marriage quality can also be affected by external sources of stress. (oureverydaylife.com)
The school now uses its website as the main lead generation tool and no longer uses external sources for paid leads. (blog.hubspot.com)