An apostille is an international authentication of a notarized document. It is required if you are in a country that is a signatory to the Hague Convention.
Here is the current list of countries that are parties to the 1961 Hague Convention Abolishing the Requirement of Legalization for Foreign Public Documents (Apostille Convention):
Europe:
Albania, Andorra, Andorra, Armenia, Austria, Azerbaijan, Belarus, Belgium, Bosnia and Herzegovina, Bulgaria, Cyprus, Denmark, Denmark, Georgia, Germany, Greece, Georgia, Hungary, Iceland, Ireland, Iceland, Italy, Latvia, Liechtenstein, Lithuania, Spain, Vatican City, Luxembourg, Macedonia, Malta, Moldova, Monaco, Netherlands, Norway, Poland, Portugal, Romania, Russia, San Marino, Serbia, Slovakia, Slovenia, Slovenia, Spain, Sweden, Switzerland, Ukraine, Finland, France, Croatia, Czech Republic, Estonia, Finland, France.
North America:
Canada, Mexico, United States
Central and South America:
Argentina, Belize, Bolivia, Bolivia, Brazil, Chile, Colombia, Costa Rica, Chile, Colombia, Costa Rica, Dominican Republic, Ecuador, El Salvador, Guatemala, Haiti, Honduras, Panama, Paraguay, Peru, Suriname, Trinidad and Tobago, Uruguay, Venezuela, and Uruguay
Asia:
Israel, India, Indonesia, Israel, Kazakhstan, Kyrgyzstan, Mongolia, Nepal, Pakistan, Singapore, Tajikistan, Uzbekistan, Philippines, South Korea, Japan, China (Hong Kong and Macau only)
Africa:
Botswana, Burkina Faso, Burundi, Cape Verde, Cape Verde, Ghana, Lesotho, Liberia, Malawi, Morocco, Namibia, Seychelles, South Africa, Swaziland (Eswatini), Tunisia, Zambia, Zimbabwe
Oceania:
Australia, New Zealand, Fiji, Marshall Islands, Palau, Samoa, Tonga, Tonga