1. The rendering of curves or diagonal lines in a television or digital image as a series of steps. Aliasing is an artefact of the process of rasterization in television and quantization in digital media. At lower resolutions, the ‘blocky’ nature of electronic pictures begins to manifest in the form of jagged lines around diagonals and circles. Compare anti-aliasing.
2. In digital audio, a characteristic distortion caused by a low sample rate, which is unable to approximate higher frequencies.
http://www.earlevel.com/Digital%20Audio/Aliasing.html Digital audio aliasing