PAL
PAL is the television format found in most of Europe that uses 625 lines with a 50-hertz (Hz) refresh rate. If you are American and have ever traveled overseas and returned with a VHS or game console only to find it did not work properly, the reason is most likely that it transmits in PAL and not NTSC.
What is NTSC
NTSC, developed in the United States in 1953 and still the American standard as of 2011, uses a 521-line and 60-Hz format. If you try to play a PAL game, DVD or VHS tape on an NTSC television, you'll find both the video and audio distorted if it even plays at all.
Gaming and Memory Cards
Game systems, just like any other source of media that transmits through a television, must send the correct signal to the TV -- either PAL or NTSC. Similarly, memory cards must be able to store this particular type of data. PAL PS2 memory cards are made to work with PAL PlayStation/games and hold PAL content. If you plug this memory card into an NTSC PlayStation, the save files will not work, as they are save files of the PAL version of the game.
Conversion Options
Some users may never run into a conversion issue, as many televisions are meant to work with both systems as of 2011. However, if you do find yourself trying to play a PAL PlayStation on an NTSC television without luck, you have a few options. Some PlayStation games offer the option to change the output from PAL to NTSC at the very "Settings" menu (usually denoting NTSC by 60 Hz and PAL by 50 Hz). If your system doesn't allow this option, you may have a security chip installed on your particular console. This chip prevents you from playing PAL games on an NTSC PlayStation. While options to bypass the chip do exist, none are advisable, as you could easily damage the system in the process.