Many people get confused about the difference between the Republic of Ireland and Northern Ireland.
There are several important differences between the two. While both are located on the same island, the Republic of Ireland is located in the southern part, and, as the name implies, Northern Ireland is located in the northern part.
The Republic of Ireland is much larger than the smaller territory of Northern Ireland. Additionally, the republic is also its own country, whereas Northern Ireland is part of the UK, along with England, Scotland, and Wales.
The Republic of Ireland is a member of the European Union and has adopted the euro as its currency. As part of the UK, Northern Ireland is also a member of the European Union, but uses the British pound.
When traveling from the Republic of Ireland to Northern Ireland, make sure to bring your passport with you. It may not be checked, but it is still a good idea to have it.