NTSC stands for "National Television Standards Committee." It's a video format. There are several in the world. Japan and the US use NTSC. A large part of Europe uses PAL. France uses SECAM. There's a few more.
NTSC: 525 lines, 29.97 FPS.
PAL: 625 lines, 25 FPS.
People argue about which is better--NTSC has a higher refresh rate, PAL is higher resolution but slower.
You don't need a mod chip to display Japanese NTSC video on your TV, but your game system most likely needs a chip to play Japanese games because that's the way most systems (excluding the Nintendo DS, surprisingly) are designed. Anyway, hope that answered any possible questions you had.