An English-speaking country is a country where English is the majority language. There are some clear-cut examples, and other borderline cases. In some of these countries, there are regions where English is a second language.
The major English-speaking countries are Australia, Canada, the Republic of Ireland, New Zealand, the United States and the United Kingdom. There are several additional English-speaking countries in the West Indies (although often the main dialect is a version of non-standard English), and in Africa, where there are also indigenous languages and English is used mainly as a lingua franca.