Definition - What does Content Filtering mean?
Content filtering, in the most general sense, involves using a program to prevent access to certain items, which may be harmful if opened or accessed. The most common items to filter are executables, emails or websites. Content filters can be implemented either as software or via a hardware-based solution.
Techopedia explains Content Filtering
Content filtering works by matching strings of characters. When the strings match, the content is not allowed through. Content filters are often part of Internet firewalls. In such a usage content filtering is serving a security purpose, but content filtering is also used to implement company policies related to information system usage. For example, it's common to filter websites containing pornographic materials or social-networking sites unrelated to work.