SEO: Search engine optimization is the process of affecting the online visibility of a website or a web page in a web search engine's unpaid results.

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SEM: Search engine marketing is a form of Internet marketing that involves the promotion of websites by increasing their visibility in search engine results pages (SERPs) primarily through paid advertising.

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PPC: Pay-per-click, also known as cost per click (CPC), is an internet advertising model used to direct traffic to websites, in which an advertiser pays a publisher (typically a website owner or a network of websites) when the ad is clicked.