NTSC is the standard used for images on television sets in the US, Canada, Japan, South Korea, and some countries in Latina America. NTSC stands for National Television System Committee, a committee established by the Federal Communications Commission in 1940 to develop the technical standards for image projection on TVs.

The NTSC standard is 29.97 frames of video per second. Each frame has 525 lines of video (only 484 of which are used for the image, the rest are for tracking, captioning, etc). The PAL standard is 25 frames of video per second with 625 lines of video per frame (so it produces a better image).

VHS refers to a standard for videocassettes, while NTSC in a standard for television. However, VHS tapes are either formatted for conform to the NTSC, SECAM or PAL standards so that they will work with the televisions that the VCRs are attached to. NTSC tapes will not work with a PAL TV and vice versa. There are companies that will convert a NTSC tape to PAL format – and there are some VCRs that can play a NTSC tape on a PAL TV (in essence doing the conversion themselves), but this is not standard.

For more information, check out:
Wikipedia: NTSC
Wikipedia: PAL

An update from a Radical Reference member in Australia:

Most modern television sets and video players can view
both formats as the physical tapes are the same. NTSC colour tends to look
'dull' to those who are used to PAL.

Even if a television is incompatible, you can still view the tape, however
it will just appear in black and white only.