What is the Difference Between Similar But Different Things, Terms, and Objects

What is the Difference between UK, Britain, Republic of Ireland and Northern Ireland

This world is divided into many countries. If we look at the map of world, we can see a large portion is covered by water. Land is divided into many small and large countries. Some islands can also be seen. Every country has a particular official name. Some Countries are called with more than one name. People often get confused when they talk about UK, Britain, Ireland and Northern Ireland. Here we are describing difference between them.