Metaphysics investigates principles of reality transcending those of any particular science. Cosmology and ontology are traditional branches of metaphysics. It is concerned with explaining the fundamental nature of being and the world. Someone who studies metaphysics would be called either a "metaphysician" or a "metaphysicist".

Pay per click (PPC) is an internet advertising model used on websites, in which advertisers pay their host only when their ad is clicked. With search engines, advertisers typically bid on keyword phrases relevant to their target market. Content sites commonly charge a fixed price per click rather than use a bidding system.

Cost per click (CPC) is the amount of money an advertiser pays search engines and other Internet publishers for a single click on its advertisement that brings one visitor to its website.

The word "skyscraper" originally was a nautical term referring to a tall mast or its main sail on a sailing ship. The term was first applied to buildings in the late 19th century as a result of public amazement at the tall buildings being built in Chicago and New York City. The traditional definition of a skyscraper began with the "first skyscraper", a steel-framed ten-storey building. Chicago's now demolished ten-storey steel-framed Home Insurance Building (1885) is considered the "first skyscraper".

Shakespeare produced most of his known work between 1589 and 1613. His early plays were mainly comedies and histories, genres he raised to the peak of sophistication and artistry by the end of the sixteenth century. He then wrote mainly tragedies until about 1608, including Hamlet, King Lear, and Macbeth, considered some of the finest works in the English language. In his last phase, he wrote tragicomedies, also known as romances, and collaborated with other playwrights. Many of his plays were published in editions of varying quality and accuracy during his lifetime. In 1623, two of his former theatrical colleagues published the First Folio, a collected edition of his dramatic works that included all but two of the plays now recognised as Shakespeare's.

Webmasters and content providers began optimizing sites for search engines in the mid-1990s, as the first search engines were cataloging the early Web. Initially, all a webmaster needed to do was submit the address of a page, or URL, to the various engines which would send a spider to "crawl" that page, extract links to other pages from it, and return information found on the page to be indexed. The process involves a search engine spider downloading a page and storing it on the search engine's own server, where a second program, known as an indexer, extracts various information about the page, such as the words it contains and where these are located, as well as any weight for specific words, and all links the page contains, which are then placed into a scheduler for crawling at a later date.

Site owners started to recognize the value of having their sites highly ranked and visible in search engine results, creating an opportunity for both white hat and black hat SEO practitioners. According to industry analyst Danny Sullivan, the phrase search engine optimization probably came into use in 1997.

During the Middle Ages, fortified castles were built by feudal nobles to mark their powers against their rivals. When King Philip II took Rouen from King John, for example, he demolished the ducal castle to build a bigger one. Fortified cities were also common, unfortunately most French castles did not survive the passage of time. This is why Richard the Lionheart's Château-Gaillard was demolished, as well as the Château de Lusignan. Some important French castles that survived are Chinon, Château d'Angers, the massive Château de Vincennes and the so called Cathar castles.

Modern physics describes gravitation using the general theory of relativity, in which gravitation is a consequence of the curvature of spacetime which governs the motion of inertial objects. The simpler Newton's law of universal gravitation provides an accurate approximation for most calculations.

The terms gravitation and gravity are mostly interchangeable in everyday use, but a distinction is made in scientific circles. "Gravitation" is a general term describing the phenomenon by which bodies with mass are attracted to one another, while "gravity" refers specifically to the net force exerted by the Earth on objects in its vicinity as well as by other factors, such as the Earth's rotation.

The International Space Station (ISS) is a research facility currently being assembled in Low Earth Orbit. On-orbit construction of the station began in 1998, and is scheduled to be complete by 2011, with operations continuing until around 2015. As of 2009, the ISS is the largest artificial satellite in Earth orbit, larger than any previous space station.

As the number of sites on the Web increased in the mid-to-late 90s, search engines started appearing to help people find information quickly. Search engines developed business models to finance their services, such as pay per click programs offered by Open Text in 1996 and then Goto.com in 1998. Goto.com later changed its name to Overture in 2001, and was purchased by Yahoo! in 2003, and now offers paid search opportunities for advertisers through Yahoo! Search Marketing. Google also began to offer advertisements on search results pages in 2000 through the Google AdWords program. By 2007, pay-per-click programs proved to be primary money-makers for search engines.

Search engine optimization consultants expanded their offerings to help businesses learn about and use the advertising opportunities offered by search engines, and new agencies focusing primarily upon marketing and advertising through search engines emerged. The term "Search Engine Marketing" was proposed by Danny Sullivan in 2001 to cover the spectrum of activities involved in performing SEO, managing paid listings at the search engines, submitting sites to directories, and developing online marketing strategies for businesses, organizations, and individuals.