Internet advertising model used to direct traffic to websites, in which an advertiser pays a publisher when the ad is clicked. Pay-per-click is commonly associated with first-tier SE.

A software system that is designed to search for information on the World Wide Web. The search results are generally presented in a line of results often referred to as search engine results pages.

A web application that people use to build social networks or social relations with other people who share similar personal or career interests, activities, backgrounds or real-life connections.

A content management system (CMS) manages the creation and modification of digital content. It typically supports multiple users in a collaborative environment. CMS features vary widely.