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A Component is a functionally independent part of any system. It performs some function and may require some input or produce some output. A component can be either a software component. A Software Component is software program or module that contains computer instructions to be executed, e.g., an operating system, Internet application, or device driver.
Source: https://www.techopedia.com/definition/3217/component
See also: https://www.first.org/cvss/user-guide#Glossary-of-Terms