There are very technical explantions of PAL and NTSC, which you can easily find by searching in google.  However if like me a simple explanation will suffice then this is my Guide.

DVD format & Regions

DVD Format (PAL or NTSC)

This is related to the image that is created on the screen, and links back to the development of TV around the world, where different countries decided on different type of broadcast type.  Format is related to regions, as I believe that regions always have either one type of format.  i.e. all Region 1 countries are NTSC format and all Region 2 countries are PAL

Therefore even though a disc may be unrestricted you need to check if the format it is in is correct for your TV.  In Europe most modern TVs and DVD players can automatically convert the signal to the correct version to be viewed on the screen.  This is not as common in the USA/Canada.  It is advised that if you wish to play a DVD or Game that is PAL format, you check both your DVD, Game Console or TV manuals to see if it can convert.

PAL Countries

If you type PAL NTSC into Wikipedia is gives a guide to which countries take which format.

Regions

Regions (i.e. Region 2) were introduced by manufacturers of DVDs to create pricing stability of DVDs.  They wanted to ensure that DVDs retailed in certain countries with lower cost bases would not be able to work in countries with higher costs (This is my view anyway).  There is software in the DVD which detects your DVD player, and stops it from playing.  People get round this with the use of Region Free DVD players, or by playing on Computers.

Regions   
1     US, US territories and Canada     American Samoa, Canada, Guam, Palau, Mariana Islands, Marshall Islands, Puerto Rico, Micronesia, United States, U.S. Virgin Islands

2     UK, Europe, Japan, South Africa and Middle East     Albania, Andorra, Austria, Bahrain, Belgium, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, Denmark, Egypt, Finland, France, Germany, Gibraltar, Greece, Greenland, Hungary, Iceland, Iran, Iraq, Ireland, Israel, Italy, Japan, Jordan, Kuwait, Lebanon, Liechtenstein, Luxembourg, Macedonia, Malta, Moldova, Monaco, Netherlands, Norway, Oman, Poland, Portugal, Qatar, Romania, San Marino, Saudi Arabia, Slovakia, Slovenia, South Africa, Spain, Sweden, Switzerland, Syria, United Arab Emirates, United Kingdom, Vatican City, Yemen, Yugoslavia

3     Southeast and East Asia     Cambodia, Hong Kong, Indonesia, Laos, Malaysia, Myanmar, Phillipines, South Korea, Taiwan, Thailand, Vietnam

4     Australia, New Zealand, Central and South America     Antigua, Argentina, Aruba, Australia, Bahamas, Barbados, Barbuda, Belize, Bolivia, Brazil, Chile, Colombia, Costa Rica, Cuba, Dominica, Dominican Republic, Ecuador, El Salvador, Falkland Islands, French Guiana, Grenada, Guatemala, Guyana, Haiti, Honduras, Jamaica, Mexico, New Guinea, New Zealand, Nicaragua, Panama, Paraguay, Peru, Suriname, Trinidad, Tobago, Uruguay

5     Former Soviet Union, Indian sub-continent, Africa, North Korea and Mongolia     Afghanistan, Algeria, Angola, Bangladesh, Belarus, Benin, Botswana, Burkina Faso, Burundi, Cameroon, Cape Verde, Central African Republic, Chad, Comoros, Congo, Djibouti, Equatorial Guinea, Eritrea, Estonia, Ethiopia, Gabon, Gambia, Georgia, Ghana, Guinea, Guinea-Bissau, India, Ivory Coast, Kazakhstan, Kenya, Latvia, Lesotho, Liberia, Libya, Lithuania, Madagascar, Malawi, Mali, Mauritania, Mauritius, Mongolia, Morocco, Mozambique, Namibia, Niger, Nigeria, North Korea, Pakistan, Russia, Rwanda, Sao Tome and Principe, Senegal, Seychelles, Sierra Leone, Somalia, Sri Lanka, St. Helena, Sudan, Tanzania, Togo, Tunisia, Turkmenistan, Uganda, Ukraine, Uzbekistan, Zambia, Zimbabwe

6     China     China
7     Reserved for future use    
8     International Territories (ships, planes etc)
0     Region Free - Unrestricted    World Wide usage

I hope this has been a useful guide.  Please click that you found it useful if it was. Thanks