What's The Meaning Of De, Do, Da And Dos?

de means "of"
do means "of the" (masculine noun)
da means "of the" (feminine noun)
dos plural "of the" (masculine nouns)

For example:

Quinta de Vargellas: Quinta of Vargellas (the name of the place)

Quinta de Terra Feita: Quinta of finished/prepared earth

Quinta do Panascal: Quinta of the grazing pastures

Quinta do Cruzeiro: Quinta of the Cross/Monument

Quinta da Roeda: Quinta of Roeda (the name of the place)