Bit depth

Audio
Bit depth (aka "word length") fixes the encoded dynamic range of an audio event or item. 24-bit audio provides a dynamic range that approaches the limits of the dynamic ranges of sound encountered in nature; in contrast, 16-bit audio, the CD standard, may be inadequate for many types of material especially where high-level transients are encoded, such as the transfer of damaged discs.

Image
Bit depth (also referred to as color depth) is the number of bits used to represent each pixel in an image. The term can be confusing since it is sometimes used to represent bits per pixel and at other times, the total number of bits used multiplied by the number of total channels. For example, a typical color image using 8 bits per channel is often referred to as a 24-bit color image (8 bits x 3 channels). Color scanners and digital cameras typically produce 24-bit (8 bits x 3 channels) images or 36-bit (12 bits x 3 channels) capture, and high-end devices can produce 48-bit (16 bit x 3 channels) images. A grayscale scanner would generally be 1 bit for monochrome or 8 bit for grayscale (producing 256 shades of gray).