# Depth

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**depth psychology**— n. any system of psychology, as psychoanalysis, dealing with the processes of the unconscious …82

**depth of definition**— depth of focus 1 …83

**depth indicator**— depth indicator, = fathometer. (Cf. ↑fathometer) …84

**Depth of field**— The area within the depth of field appears sharp, while the areas in front of and beyond the depth of field appear blurry …85

**Depth charge**— For other uses, see Depth charge (disambiguation). Mark IX Depth Charge used by the U.S. Navy late in World War II. Unlike the cylindrical, barrel shaped depth charge used earlier, the Mark IX is streamlined and equipped with canted fins to… …86

**Depth in a well**— In the oil and gas industry, depth in a well is the measurement, for any point in that well, of the distance between a reference point or elevation, and that point. It is the most common method of reference for locations in the well, and… …87

**Depth of noncommutative subrings**— In ring theory and Frobenius algebra extensions, fields of mathematics, there is a notion of depth two subring or depth of a Frobenius extension. The notion of depth two is important in a certain noncommutative Galois theory, which generates Hopf …88

**Depth of focus**— For the seismology term, see Depth of focus (tectonics). Depth of focus is a lens optics concept that measures the tolerance of placement of the image plane (the film plane in a camera) in relation to the lens. In a camera, depth of focus… …89

**Depth (ring theory)**— In commutative and homological algebra, depth is an important invariant of rings and modules. Although depth can be defined more generally, the most common case considered is the case of modules over a commutative Noetherian local ring. In this… …90

**Depth map**— This article is about techniques which relate to recording distances from a viewpoint. For modifying the geometry of surfaces or the illusion of this in computer graphics, see Heightmap and Bump mapping. In 3D computer graphics a depth map is an… …