Final answer:
Squid is an open-source software that functions as a proxy server, used primarily for web caching and can also function as a security measure.
Step-by-step explanation:
Squid is an open-source software that operates as a proxy server. This means it serves as an intermediary for users who are requesting resources from other servers. Squid can be used for a variety of tasks, but it is most commonly used for web caching. This helps to speed up web browsing and reduce bandwidth usage by storing frequently accessed web content. It can also be utilized for security purposes, allowing administrators to restrict web access.
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