As nouns the difference between fido and fado

is that fido is a coin that is defective, having been incorrectly minted, often prized by collectors while fado is a Portuguese folk song, usually featuring a single vocalist, Portuguese guitar and sometimes classical guitar. Lyrical themes are often melancholic in nature; the structure of the song is of greater importance.

As a proper noun Fido

is A representative given name for a dog.