A puro is made entirely from one country’s tobacco. A Nicaraguan puro means every leaf is Nicaraguan, and a Cuban puro means the same for Cuba. In everyday Spanish the word simply means cigar; in English-language trade use it means single-country.
It is not a mark of quality. A puro can be cheap or carefully made, and so can a blend that combines Dominican filler with an Ecuadorian wrapper. Padrón’s main lines are Nicaraguan puros made from Cuban-seed tobacco, and Fuente’s OpusX is a Dominican puro. These are facts about how the cigars are made, not a ranking.
See puro vs blend for the comparison, and cuban cigar for Cuban cigars.