NTSC's images are composed of 525 lines and NTSC displays 30 frames (complete images) per second. PAL's images are composed of 625 lines and PAL displays 25 frames per second. There are technical differences in the way color is reproduced, but the above is the basic explanation.

A TV picture is made up of lines which are switched on and off very quickly. A complete picture is called a "frame" and a frame is composed of two "fields" which are being alternated in rapid succession. This is known as the scanning frequency. The two separate TV systems came about because of the differences in power systems between the US and Europe. For various technical reasons in the early days of TV the scanning frequency was locked together with the power frequency. The US uses a 60Hz power system, therefore the NTSC TV system comprises 60 fields per second, or 30 frames per second. Europe uses a 50Hz power system, so a PAL TV picture is composed of 50 fields per second, or 25 frames per second. This is just one difference, though. There is also a difference in the number of scanlines a TV picture comprises. An NTSC picture is 525 lines whereas a PAL picture is 625 lines. Not only that but there are differences in way each system reproduces colour. When the NTSC (National Television Standards Commitee) system was first formalised in 1941 there was no provision for colour transmission. Later, when the time came to add colour to the system the engineers had to make sure that older black and white TVs could still receive a picture. Therefore the colour part of the NTSC system is a bit of a "hack", in that it was dropped on top of the black and white signal, meaning that, even to this day, colour reproduction is somewhat hit and miss. Amongst video professionals NTSC can stand for "Never Twice the Same Colour". PAL, on the other hand, was developed specifically with colour transmission in mind. PAL stands for Phase Alternating Line, which basically means that colour information is reversed on each alternating scanline, effectively cancelling out phase errors. In other words NTSC TVs need a tint control to correct for phase errors, whereas PAL TVs do this automatically. For this reason PAL is seen as the superior TV system. For the record there are other less widely used TV standards. SECAM was developed by the French, who initially wanted a system that wasn't compatible with either PAL or NTSC. For this reason SECAM was mostly adopted by Communist East European countries who wanted to keep their TV transmissions secret. It's based on the PAL 625/50 system but with a slightly different (and inferior) method of colour reproduction. PAL-M and PAL-N are the others, largely used in South America. PAL- M is based on the NTSC system of 525 lines/60Hz but uses superior PAL colour encoding. PAL-N is a 625 line/50Hz system with PAL colour encoding but with some similarities to NTSC in the way that colour is reproduced, making it a separate standard. Edit: Ok, the last sentence of a 500 word answer contains an error so you rate the WHOLE THING "incorrect". A little harsh, don't you think? Not to mention that the last two paragraphs contain some additional information that I threw in which doesn't directly relate to the question. You are right, I was wrong about PAL-N and I have made the correction, but jeez, talk about being hard to please!

Don't kill me when I say this, but the PAL system is fair superior to the NTSC's system. The picture quality is just so much better. I live in Australia, which has the PAL format, but have traveled to the States a couple of times. The two things that really caught my eye, are how many commercials’ you have, and the poor colour quality on most television sets including brand new ones.

The definition for PAL-M is correct but for PAL-N it is uncompleted: Argentina, Uruguay and Paraguay are 50Hz electical energy countries that opted for European video syncronism, that means 50 fields/25 frames of 625 lines but the tv channel radio frequencies in all the American continent is only 6Mhz so the colour carrier had to conform in the class of 3.58mhz instead of the european 4.43Mhz. Thas it. Chile is another 50Hz country but opted for the NTSC 60fields per second TV system because already was using b&w 60Hz TV.