Both PAL and NTSC are video formats.
PAL is the format used in Australia, parts of Asia, and some European countries. PAL stands for Phase Alternation Lines (625 lines) and offers more picture detail and wider luminance (color signal) bandwidth. PAL has been adopted by almost all 50 Hz countries in the world.
NTSC is the format used in the United States and Canada. NTSC stands for National Television Standard Committee which established the American TV broadcast TV standard as a 525 line broadcast. The NTSC system has higher frame rate (60 Hz) which reduces visible flicker and picture noise.
PAL delivers a scanning/frame rate of 25 fps (frames per second) with 625 lines, while NTSC delivers a scanning/frame rate of 29.97 fps using 525 lines. A TV signal is made from interlaced half-frames, hence the 25 fps in 50 Hz countries, and 30 fps in 60 Hz countries. The color information of the signal is also encoded differently. Although most TVs have the ability to display both 50 and 60 Hz signals, without proper decoding of the PAL or NTSC signal the color information will be lost and the picture appears black and white. These technical differences are the reason for an intrinsic incompatibility of PAL and NTSC DVDs/DVD Players/TVs/Games/Games consoles.
Most DVDs and ALL games sold by dvdorchard are designed for PAL systems and will not work with NTSC systems (unless you have a PAL converter). Most if not all DVD Players sold in Australia are PAL/NTSC compatible - check with your manufacturer; Most TVs sold recently in Australia are Multi System - PAL/NTSC compatible - but once again check with your manufacturer. All Games and Games Consoles sold in Australia are PAL only.
A problem that is indirectly related to PAL and NTSC is the power supply. Countries that use the PAL standard usually have AC current of 50 Hz, with voltages of 220 V or more. In contrast, countries that use the NTSC system use AC current of 60 Hz, with voltages of around 100-120 V. This means that if you intend to buy a peice of electrical equipment from a different country, you may need a voltage converter (a step-up or step-down transformer, respectively).