A review is an evaluation of a publication, service, or company such as a movie (a movie review), video game, musical composition (music review of a composition or recording), book (book review); a piece of hardware like a car, home appliance, or computer; or an event or performance, such as a live music concert, play, musical theater show, dance show, or art exhibition. In addition to a critical evaluation, the review’s author may assign the work a rating to indicate its relative merit. More loosely, an author may review current events, trends, or items in the news. A compilation of reviews may itself be called a review. The New York Review of Books, for instance, is a collection of essays on literature, culture, and current affairs. National Review, founded by William F. Buckley, Jr., is an influential conservative magazine, and Monthly Review is a long-running socialist periodical. In the scientific literature, review articles are a category of scientific paper, which provides a synthesis of research on a topic at that moment in time. A compilation of these reviews forms the core content of a ‘secondary’ scientific journal, with examples including Annual Reviews, the Nature Reviews series of journals and Trends. A peer review is the process by which scientists assess the work of their colleagues that has been submitted for publication in the scientific literature. A software review is also a form of peer review, by the co-workers. A consumer review refers to a review written by a consumer for a product or a service based on her experience as a user of the reviewed product. Popular sources for consumer reviews are e-commerce sites like Amazon or Zappos, and social media sites like TripAdvisor and Yelp. E-commerce sites often have consumer reviews for products and sellers separately. Usually, consumer reviews are in the form of several lines of texts accompanied by a numerical rating. This text is meant to aid in shopping decision of a prospective buyer. A consumer review of a product usually comments on how well the product measures up to expectations based on the specifications provided by the manufacturer or seller. It talks about performance, reliability, quality defects, if any, and value for money. Consumer review, also called ‘word of mouth’ and ‘user generated content‘ differs from ‘marketer generated content’ in its evaluation from consumer or user point of view. Often it includes comparative evaluations against competing products. Observations are factual as well as subjective in nature. Consumer review of sellers usually comment on service experienced, and dependability or trustworthiness of the seller. Usually, it comments on factors such as timeliness of delivery, packaging and correctness of delivered items, shipping charges, return services against promises made, and so on. An expert review usually refers to a review written by someone who has tested several peer products or services to identify which offers the best value for money or the best set of features. A bought review is the system where the creator (usually a company) of a new product pays a reviewer to review his new product.