In general, the term bitmap refers to an image formed by a pattern of bits, rather than by a pattern of lines. In Windows, there are two kinds of bitmaps:
A device-dependent bitmap is a pattern of bits, in memory, that can be displayed on an output device. Because there is a close correlation between the bits in memory and the pixels on the screen, a memory bitmap is said to be device dependent. For such bitmaps, the way the bits are arranged in memory depends on the intended output device.
A device-independent bitmap (DIB) describes the appearance of an image, rather than the way that image is represented internally by a particular display device. Because this external definition can be applied to any display device, it is referred to as device independent.