The Commonwealth of Nations is simply put, (mostly) former members of The British Empire who are still connected with the UK.
In its modern form it is more of a beneficial trade, defence and immigration pact than an empire, but about one-third of the nations also have the British monarch as their head of state, giving her the same theoretical veto powers outlined in British Political System, while the Judicial Committee of the Privy Council in London is a final court of appeal for some member states.
Member states sometimes enjoy beneficial trade agreements and the ability to emigrate to other member states more easily than a non member. Commonwealth nations tend to share such characteristics as drinking tea, playing cricket, driving on the left-hand side of the road and using British English spellings. Most of them also use The Common Law as the basis of their legal system.
Mozambique was actually never part of the British Empire, being a former Portuguese territory, but all its neighbour countries were in the Commonwealth and wished to support their poor neighbour, so an exception to the general policy was made. Recently the same thing happened to Rwanda, which has started to adopt more Anglophone trappings and apparently even cricket picked up from Kenya and Uganda.
The terms "Old Commonwealth" (the UK, Canada, Australia, New Zealand, and South Africa) and "New Commonwealth" (everywhere else) are sometimes used, although the terms appear to be declining in usage.
They have their own version of the Olympic Games, called the Commonwealth Games, held every World Cup year. The 2010 games were held in New Delhi, India, and although there was some initial concern over security, a mass case of food-poisoning seemed to be the worst thing that happened to the athletes (and if food poisoning is the worst thing to happen to you in India, you had an only slightly-worse-than-normal trip). The 2014 Commonwealth Games were held in Glasgow, and took place rather quietly for an international event.
It must be noted that one criteria for joining the commonwealth is the acceptance of the current British monarch (the Queen) as head of the commonwealth. It seems unlikely most countries that aren't current members are liable to agree to such a condition, if they were so inclined.
The list of member states are:
- Antigua and Barbuda
- The Bahamas
- Fiji (an odd case; quoting Wikipedia: "Left in 1987; rejoined in 1997; suspended on 6 June 2000; suspension lifted on 20 December 2001; again suspended on 8 December 2006 because of the 2006 Fijian coup d'état. Suspension lifted on 26 September 2014.")
- Mozambique (actually a former Portugese colony)
- New Zealand
- Papua New Guinea
- Rwanda (The second nation to be admitted without any national ties to the UK)
- Saint Kitts and Nevis
- Saint Lucia
- Saint Vincent and the Grenadines
- Sierra Leone
- Solomon Islands
- South Africa (not a member from 1961 to 1994, because of apartheid)
- Sri Lanka
- Trinidad and Tobago
- United Kingdom