Definition
The foundation of most things is known as "the base". In this case, it's no different. The base of a URL is the part on top of which all other relative URLs [→] are appended.
For example for both example.com/page/admin and example.com/page/profile, example.com is the base URL.
Summary
It is common for the domain name [↗] of most URLs to be referred to as the base URL.
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