PAL, short for phase-alternating line, phase alternation by line or phase alternation line, is a colour encoding system used in broadcast television systems in large parts of the world.

The term "PAL" is often used informally to refer to a 625-line/50 Hz (principally European) television system, and to differentiate from a 525-line/60 Hz (principally North American/Central American/Japanese) "NTSC" system. There are two more variants of PAL based on the sound system. They are PAL-M(525-line/60Hz) and PAL-N(625-line/50Hz).PAL-N is more like PAL and PAL-M is like PAL's Number of lines with NTSC's Frame rate. Accordingly, DVDs are labelled as either "PAL" or "NTSC" (referring informally to the line count and frame rate) even though technically neither of them have encoded PAL or NTSC composite colour.

NTSC is the analog television system in use in Canada, Japan, South Korea, the United States, and some other places, mostly in the Americas (see map). It is named for the National Television System(s) Committee, the industry-wide standardization body that created it.

The NTSC format or more correctly the M format; see broadcast television systems consists of 29.97 interlaced frames of video per second. Each frame consists of 484 lines out of a total of 525 (the rest are used for sync, vertical retrace, and other data such as captioning). The NTSC system interlaces its scanlines, drawing odd-numbered scanlines in odd-numbered fields and even-numbered scanlines in even-numbered fields, yielding a nearly flicker-free image at its approximately 59.94 hertz (nominally 60 Hz/1.001) refresh frequency. This compares favorably to the 50 Hz refresh rate of the 625-line PAL and SECAM video formats used in Europe, where 50 Hz alternating current is the standard; flicker is more likely to be noticed when using these standards (However, a few modern PAL TV sets use 100 Hz refresh rate to eliminate flicker, effectively displaying one frame twice, although this causes motion problems, and so has not been widely used. ). Interlacing the picture does complicate editing video, but this is true of all interlaced video formats, including PAL and SECAM.