PAL is Phase Alternating Line, a German format for color television signal. PAL spread from Germany to many countries in Eurasia, Africa and Oceania. PAL also spread to a few South American countries including Argentina, Uruguay and Brazil. With the invention of devices like video players and video game consoles, PAL devices also spread to SECAM countries.
PAL uses about 50 vertical blanks per second, so each PAL video game console must output about 50 frames per second. The source of many video games is Japan, where the NTSC video games consoles must output about 60 frames per second. The port of video game from Japan (or other NTSC country) to PAL country has problem with the change from 60 to 50 frames per second. PAL ports of NTSC games might run at 5/6 of correct speed or have other problem with frame rate.
Emulators can approximate the correct frame rate of both PAL and NTSC games. So players in PAL countries like to use emulators to play NTSC versions of games. ROM hackers sometimes prefer to hack NTSC versions, not PAL versions. There might be no choice; many NTSC games have no PAL exports.