Aperture grille: In some CRTs, the aperture grille is a series of wires stretched vertically down the inside of the monitor to mask the beams from the electron guns at the back of the tube. In other types of monitors, this function falls to a perforated metal plate called a shadow mask. Some users prefer the image quality of Sony Trinitron monitors, which use an aperture grille; others notice the faint horizontal shadows cast by the grille's tensioning wires and prefer other shadow-mask designs.

Bezel: The frame around a CRT's or LCD's screen.

Convergence: Color CRTs rely on three separate electrical beams to project simultaneous red, green, and blue images; these combine to form a full-color image. If these beams are not precisely aligned, the red, green, and blue portions of the image may not overlap correctly, degrading the overall image quality. When the three beams converge correctly at all points on the display, you get a perfect image.

CRT: Cathode-ray tube; a big bell of glass with electron guns at one end and a viewing screen at the other. Televisions and computer displays both use this imaging technology and are often simply called CRTs.

Display size: A display's length (in inches or centimeters) taken diagonally from one corner to the opposite corner. Unless it specifically states viewable screen area, a CRT's measurement encompasses the full face of the picture tube, including the part concealed by the bezel. On an LCD, only the viewable screen is measured.

Dot pitch: In CRTs, the distance from one pixel to the next-nearest one. The larger the dot pitch, the grainier an image looks.

Electron gun: A color CRT contains three electron guns that shoot electron beams, causing red (R), green (G), or blue (B) phosphors on the inside front of the screen to light up.

Footprint: The amount of space a monitor takes up on your desk, including the display and its base.

LCD: Liquid-crystal display; created by sandwiching electrically reactive, liquid-crystal material between two electrodes. The substance can be darkened or lightened by applying and removing current.

Liquid crystal: A material with some of the properties of solid crystals, such as diamonds, and some of the properties of liquids, such as water. As a result, the material can both flow as well as affect the path of light, depending on how the individual molecules are aligned.

Molecule: The smallest portion of a material. For some materials, the physical size and shape of the individual molecules affect the overall properties of the material. For example, the individual molecules of liquid-crystal material can alter the path of light and can be induced to align in specific ways in response to physical or electrical influences. It is these characteristics that make them useful in creating displays.

Native resolution: The physical structure of some types of displays, including LCDs and plasma panels, defines how many pixels can be displayed at once. The display produces the sharpest picture when used at its so-called native resolution. Other types of displays, such as CRTs, create pixels independently of the physical structure of their screens and do not have a native resolution. As a result, a CRT's image quality is generally the same across a range of resolutions.  

Nits: A unit of measure for luminance (a monitor's brightness); equivalent to candelas per square meter (cd/m²).

Phosphor: A substance that can produce red, green, or blue light when excited by an energy source, such as the electron beam in a CRT. Phosphors are arranged as either dots or stripes on the inside face of a CRT screen.

Pixel: In a CRT, phosphors grouped in RGB triads (one each of red, green, and blue) are called pixels. The hundreds of thousands to millions of pixels in a display create images.

Refresh rate: The frequency at which a CRT's electron guns redraw the image; measured in hertz (Hz). One hertz equals one cycle per second; a 70Hz refresh rate means that the entire screen is redrawn 70 times per second.

Resolution: For both CRTs and LCDs, the number of pixels in the whole image. For example, a resolution of 1,280x1,024 pixels means that 1,024 lines are drawn from the top to the bottom of the screen, and each of these lines is made up of 1,280 separate pixels.

Screen geometry: A description of how accurately lines and shapes are represented on the display. LCDs almost always have perfect geometry because the display information is mapped to specific physical pixels on the display. CRTs may have problems with screen geometry; larger screens and flat-faced models have particular difficulty controlling electron beams with precision. As a result, vertical lines may be noticeably curved at the edges of the display, and circles may appear oval or egg-shaped. The best CRT monitors include controls that let you adjust the screen geometry; still, it can be difficult to adjust it perfectly in all regions of the screen.

Shadow mask: A metal plate with holes in it that selectively blocks the beams from the electron guns in the back of a CRT.

Stripe pitch: Monitors using an aperture grille or a striped mask have phosphors arranged in vertical stripes. Stripe pitch is the distance from a stripe of a given color to the next stripe of the same color. A smaller stripe pitch means that the monitor can display higher-resolution images more accurately.

Stuck/dead pixel: A pixel on an LCD that is either permanently on (stuck) or permanently off (dead).

Subpixel: Full-color displays are made by combining red, green, and blue light in varying degrees to produce different shades of colors. In a display with a fixed pixel structure, such as LCDs or plasma panels, the red, green, and blue light comes from adjacent cells in the display's physical structure. The light from these three subpixels--one for each color--combine to create a single pixel. There are also pixel structures that do not rely on three subpixels.

SVGA: Supervideo graphics array; a display mode with a resolution of 800x600 pixels.

TFT: Thin-film transistor; refers to the switching devices placed in each liquid-crystal cell in an active-matrix LCD. TFT screens are brighter and more readable than passive-matrix LCDs, but they consume more power and are generally more expensive.

Trinitron: A type of CRT developed by Sony that differs from standard tube types in that it employs an aperture grille instead of the usual shadow mask.

SXGA: Superextended graphics array; a display mode with a resolution of 1,280x1,024 pixels.

UXGA: Ultraextended graphics array; a display mode with a resolution of 1,600x1,200 pixels.

VGA: Video graphics array; a display mode with a resolution of 640x480 pixels.

Viewable area: The diagonal length of a CRT's viewable screen.

XGA: Extended graphics array; a display mode with a resolution of 1,024x768 pixels.