(1) Dot is the same as the period character (.). In DOS, Windows, and OS/2 systems, the dot is used to separate a filename from its extension. For example, the filename CONFIG.SYS is pronounced config-dot-sys.
(2) In bit-mapped representations, a dot is a single point, the smallest identifiable part of an image. Laser printers, for example, create characters and images by printing patterns of dots. Likewise, monitors display images as arrays of dots. The resolutions of devices are often measured in dots per inch (dpi).
(3) In computer gaming DOT means damage over time.