Name Description
Gain: Gain defines how many electrons are represented by each Analog to Digital Unit (ADU). A gain of 4 means that the A/D converter has digitized the signal so that each ADU corresponds to 4 electrons. DSLR cameras can change ISO by changing the gain.
Gamma Correction: Gamma correction is used to alter the output levels of a display. Since the standard input signal (or voltage level) is not high enough to create a bright picture, gamma correction is used to boost the brightness and contrast of the display. PCs typically use a gamma setting of 2.2, while Macs have a default gamma setting of 1.8. Some systems include a display utility that can be used to apply custom gamma settings.
Gamma: In photography, gamma refers to the midtone contrast of an image. Technically, gamma refers to the relationship between input voltage and output intensity, where gamma is the exponent in a power-law relationship between input values and output displayed brightness, such as in a computer monitor.
Gamut: The range of colors that can be detected, recorded or displayed by an imaging device. Each device has a unique gamut.
Ghosting: A shadow or weak secondary image as seen on a monitor or display which is created by multiple path broadcast transmission errors.
Gigabyte: A gigabyte is 2 to the 30th power, or 1,073,741,824 bytes.

It can be estimated as 10 to the 9th power, or one billion (1,000,000,000) bytes. A gigabyte is 1,024 megabytes and precedes the terabyte unit of measurement. Hard drive sizes are typically measured in gigabytes, such as a 160GB or 250GB drive. The term gigabyte is often often abbreviated as simply a "gig" in speech.
GPS Stands for "Global Positioning System." GPS is a satellite navigation system used to determine ground position and velocity (location, speed, and direction). Though it was created and originally used by the U.S. military, GPS is now available to the general public all over the world. GPS navigation systems are currently installed in a number of luxury cars, complete with an LCD map that shows the driver exactly where in the world he is.
GPU: Stands for "Graphics Processing Unit." Like the CPU (Central Processing Unit), it is a single-chip processor. However, the GPU is used primarily for computing 3D functions. This includes things such as lighting effects, object transformations, and 3D motion. Because these types of calculations are rather taxing on the CPU, the GPU can help the computer run more efficiently.
Graphic Tablet: A graphics tablet or digitizer is a computer input device that enables a user to hand-draw images, animations and graphics, similar to the way a person draws images with a pencil and paper. These tablets may also be used to capture data or handwritten signatures. It can also be used to trace an image from a piece of paper which is taped or otherwise secured to the surface. Capturing data in this way, by tracing or entering the corners of linear poly-lines or shapes, is called digitizing.
Graphics: Computer graphics are images displayed on a computer screen. They can be either two or three-dimensional. Two-dimensional graphics come in raster or vector formats.

Raster graphics are the most common type of computer graphic and are used for icons, photos, and other basic images. Vector graphics are used for drawings, logos, and other scalable objects. 3D graphics are made up of polygons and can be created with CAD and 3D modeling programs. They are most commonly seen in video games and 3D animations.
GUI: Stands for "Graphical User Interface," and is pronounced "gooey." It refers to the graphical interface of a computer that allows users to click and drag objects with a mouse instead of entering text at a command line. Two of the most popular operating systems, Windows and the Mac OS, are GUI-based.