Website categorization can be used for:
Personalization (e.g. show relevant headline based on the industry).
Database enrichment (e.g. enrich user profiles).
Content filtering (e.g. ban websites from specific industries).
SIC stands for "Standard Industrial Classification" and its initial purpose was to create a standard various government agencies could use. The SIC standard hasn't been updated since 1987, but it is still in use by some areas of the government (e.g. SEC).
NAICS is an acronym for the North American Industry Classification System and its purpose is to create an industry standard to categorize & compare businesses in the US, Canada, and Mexico. The NAICS standard focuses on the primary sector and is revised each every five years (the latest version is 2017).
IAB (Interactive Advertising Bureau) is a trade group representing online publishers and advertisers. They help establish industry best practices by developing various standards such as the IAB Taxonomy.
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