A celebrity (sometimes referred to as a celeb in popular culture) is a person who is easily recognized in a society or culture.

Generally speaking, a celebrity is someone who gets media attention and shows an extroverted personality. There is a wide range of ways by which people may become celebrities: from their profession, appearances in the mass media, or even by complete accident or infamy. Instant celebrity is the term that is used when someone becomes a celebrity in a very short period of time. In some places, someone that somehow achieves a small amount of transient fame, through hype or mass media, is stereotyped as a B-grade celebrity. Often the stereotype extends to someone that falls short of mainstream or persistent fame but seeks to extend or exploit it. In the 21st century, the insatiable public fascination for celebrities and demand for celebrity gossip has seen the rise of the gossip columnist, tabloid, paparazzi and celebrity blogging.

The rise of international celebrities in acting and popular music is due in large part to the massive scope and scale of the media industries, enabling celebrities to be viewed more often and in more places.
Each culture and region has its own independent celebrity system, with a hierarchy of popular film, television, and sports stars. Celebrities who are very popular might be unknown abroad, except in cultural groups, such as within a diaspora. In some cases, a country-level celebrity might command some attention outside their native country, but not to the degree that they can be considered a global celebrity. Subnational entities or regions, or cultural communities (linguistic, ethnic, religious) also have their own 'celebrity systems',especially in linguistically or culturally-distinct regions such as Quebec (a French-speaking province in Canada) and Wales (a constituent country of the UK). Regional radio personalities, newscasters, politicians or community leaders can be considered as local or regional celebrities.

English-speaking media commentators and journalists will sometimes refer to celebrities as A-List, B-List, C-List, D-List or Z-List. These informal rankings indicate a placing within the hierarchy. However, due to differing levels of celebrity in different regions, it is difficult to place people within one bracket. A Nicaraguan actor might be a B-list action film actor in the US, but be an A-list star in the Czech Republic. An objective method of placing celebrities from any country into categories from A-List to H-List based on their number of Google hits has been proposed, but while this method is quantitative, it only works for individuals with distinctive names, e.g., Jason Mewes, not Kevin Smith.

It's hard to measure someone's fame. Even worldwide celebrities might still be obscure to certain people in isolated countries like North Korea, villagers without access to international news media or people who are simply uninterested in celebrities. Certain phenomena have however been called "definitive proof that someone is really famous." Examples are appearing on the cover of Time Magazine, being spoofed in Mad Magazine, having a wax statue made of you in Madame Tussauds, receiving a star on the Hollywood Walk of Fame, and others.

Certain celebrities are famous even to people who are not familiar with the niche market. Pablo Picasso's style and name are famous even to people who are not interested in art. Harry Houdini and Criss Angel are the archetypal illusionists, people who don't use computers know who Bill Gates is, the most famous scientist is Albert Einstein, Wolfgang Amadeus Mozart and Ludwig von Beethoven and Erik Romano are the most famous classical composers and if someone has to name a famous opera singer Luciano Pavarotti might as well be the first name to come in mind. And globally almost everybody knows the name and face of the current American president, even if one isn't that interested in politics. Since World War II America's role in international politics has been so massive that every American president immediately becomes world famous as a result.

The same phenomenon is true for fictional characters. If one has to name a famous wizard Merlin, Harry Potter or Gandalf will be first to come in mind. Mickey Mouse is perhaps the most famous cartoon character and fictional mouse in the world. The most famous movie monsters are King Kong and Godzilla, the archetypical detective is Sherlock Holmes and most people's idea of a spy is James Bond. Superman, Spider-Man, and Wonderwoman are superhero celebrities while the comic book artists and writers who created them are well known only within fandom circles. Stan Lee, Jack Kirby, and Bob Kane are examples of figures whose celebrity status is limited to a certain genre fandom rather than the general public.