(linguistics) A theory that posits a common syntactic structure for different lexical categories. Each phrase (XP) is the projection of a head (X) and may optionally include a specifier (sister of X-bar, daughter of XP), adjuncts (sister and daughter of X-bar) and complements (sister of X, daughter of X-bar).

(economics) Theory that the price of an object is determined by irrational beliefs and expectations of market participants, rather than intrinsic value; i.e. that one can make money by buying something for the sole reason of selling it to some one else for a higher price.

(mathematical analysis) A theorem which states that any real-valued Lebesgue integrable function can be approached arbitrarily closely from below by an upper semicontinuous function and also from above by a lower semicontinuous function.

(informal) The proposition that a monkey hitting typewriter keys at random is bound to produce meaningful text (such as a work by William Shakespeare), given an infinite amount of time.

(astronomy) A cosmological model of the universe in which matter is continuously created as the universe expands

(LGBT) A field of critical theory that emerged in the early 1990s out of LGBT studies and feminist studies, a kind of interpretation devoted to queer readings of texts.

The theory that employees are inherently lazy and irresponsible and will tend to avoid work unless closely supervised and given incentives.

The theory that employees are capable of being ambitious and self-motivated under suitable conditions.

gender studies

(philosophy) Arising before any theoretical considerations.