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A meta description is an HTML tag for a web page that describes the page briefly, summarizing it. 

Meta descriptions are read by search engines and often displayed for users. For example, the brief description for web pages you see in Google results is often pulled directly from the page’s meta description.

Most web traffic on the internet is now from mobile devices. Mobile First refers to a design philosophy that prioritizes a website’s mobile view first, rather than desktop or tablet views. All need to be completed for a website to be fully functional, but this prioritizes the view that a majority of users will see.

Refers to the speed at which the elements on a web page load. Site speed relates to ease of use, and is also a metric used by search engine algorithms in determining site health.