URL (Uniform Resource Locator) filtering is a security measure that is used to allow or block access to specific websites or categories of websites based on the URL of the website.
URL filtering works by creating a list of allowed or blocked URLs or categories of URLs. When a user tries to access a website, the URL is checked against the list. If the URL is on the allowed list, the user is granted access to the website. If the URL is on the blocked list, the user is denied access to the website.
URL filtering can be used to protect users from accessing potentially harmful or inappropriate websites, and can also be used to help enforce internet usage policies within an organization. URL filtering can be implemented at the network level, using a firewall or other security appliance, or at the user level, using a browser extension or other software.