Convention Refugees 협약난민
Refugee is who can't take protection or deny the protection of their land of citizenship. 
They are staying at out of their country because of fear from the percecution that instead of difference religion, ethnicity, or political opinion.
This definition is according to Convention Relating to the Status of Refugees

De facto refugees 사실상난민
They were not recognized as a refugee for refugee agreement.
But they did not go to mother country.

Internally Displaced Person 국내실향민
They wander in their country without nationality. 
They becamed IDP because of war mostly. In Sudan, there are 5 million IDP.

Refugee sur place 현지난민
While they are in another country, there are a military coup their country. so became did not go to motherland.