Absolutely, it was like the soy sauce of the ancient world, and apparently where Romans got their sodium intake from. For curious students, here's a quote where Isidore describes garum, from his Etymologiae:

«Garum est liquor piscium salsus, qui olim conficiebatur ex pisce quem Graeci γάρον vocabant; et quamvis nunc ex infinito genere piscium fiat, nomen tamen pristinum retinet a quo initium sumpsit».

[Garum is a salty liquid [made] from fish, which was once prepared with a fish which the Greeks called γάρον [garon]; and although it is now made from an infinite variety of fishes, the original name however is retained from the one adopted initially].