Although the origins are difficult to trace, today fado is commonly regarded as simply a form of song which can be about anything, but must follow a certain traditional structure. In popular belief, fado is a form of music characterized by mournful tunes and lyrics, often about the sea or the life of the poor, and infused with a sentiment of resignation, fatefulness and melancholia. This is loosely captured by the Portuguese word saudade, or “longing”, symbolizing a feeling of loss (a permanent, irreparable loss and its consequent lifelong damage). This is similar to the character of the music genre Morna from Cape Verde, which may be historically linked to fado in its earlier form but has retained its rhythmic heritage. This connection to the music of a historic Portuguese urban and maritime proletariat (sailors, dock workers, port traders, etc.) can also be found in Brazilian Modinha and Indonesian Kroncong, although all these music genres subsequently developed their own independent traditions.
https://en.m.wikipedia.org/wiki/Fado