Alien Passport

An Alien Passport is a travel document issued by a country to non-citizens residing within their borders who are either stateless persons, or otherwise unable to obtain a passport from their state of nationality.
These documents are not regulated by a convention, however they should meet International Civil Aviation Organisation standards for travel documents.
These documents allow a refugee to travel out of and back into the country, usually according to the rules which apply to nationals of that country, but depend on the country they are travelling from/to.
Some states refer to these documents as Certificates of Identity, Certificates of Travel, or Re-Entry Permits.