- published: 04 Mar 2016
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A definition is a statement of the meaning of a term (a word, phrase, or other set of symbols). Definitions can be classified into two large categories, intensional definitions (which try to give the essence of a term) and extensional definitions (which list every single object that a term describes). A term may have many different senses and multiple meanings, and thus require multiple definitions.
In mathematics, a definition is used to give a precise meaning to a new term, instead of describing a pre-existing term. Definitions and axioms are the basis on which all of mathematics is constructed.
An Intensional definition, also called a connotative definition, specifies the necessary and sufficient conditions for a thing being a member of a specific set. Any definition that attempts to set out the essence of something, such as that by genus and differentia, is an intensional definition.
An extensional definition, also called a denotative definition, of a concept or term specifies its extension. It is a list naming every object that is a member of a specific set.
YouTube is a video-sharing website headquartered in San Bruno, California, United States. The service was created by three former PayPal employees in February 2005. In November 2006, it was bought by Google for US$1.65 billion. YouTube now operates as one of Google's subsidiaries. The site allows users to upload, view, rate, share and comment on videos, and it makes use of WebM, H.264/MPEG-4 AVC, and Adobe Flash Video technology to display a wide variety of user-generated and corporate media video. Available content includes video clips, TV clips, music videos, movie trailers and other content such as video blogging, short original videos, and educational videos.
Most of the content on YouTube has been uploaded by individuals, but media corporations including CBS, the BBC, Vevo, Hulu, and other organizations offer some of their material via YouTube, as part of the YouTube partnership program. Unregistered users can watch videos, and registered users can upload videos to their channels. Videos considered to contain potentially offensive content are available only to registered users affirming themselves to be at least 18 years old.
2011 (MMXI) was a common year starting on Saturday (dominical letter B) of the Gregorian calendar, the 2011th year of the Common Era (CE) and Anno Domini (AD) designations, the 11th year of the 3rd millennium, the 11th year of the 21st century, and the 2nd year of the 2010s decade.
2011 was designated as:
It was marked by a wave of revolutions in the Arab World known as the Arab Spring, including the beginnings of several unresolved protest movements and armed conflicts.