This is the 7108th most frequent Russian word.
болгария
"Bолгария" translates to "Bulgaria," a country in Eastern Europe.
In this sentence, 'Болгария' is used as a proper noun to denote the country, fulfilling a nominative subject role.
Болгария - это страна в Европе.
Bulgaria is a country in Europe.
Here, 'Болгарии' is the locative form of 'Болгария', used after the preposition 'в' to indicate location.
Каждое лето мы отдыхаем в Болгарии.
Every summer we vacation in Bulgaria.
In this instance, 'Болгарии' is the genitive form of 'Болгария', showing possession as it relates to the culture of Bulgaria.