This phrase actually classifies what the following words represent. In English, such a classifying term can often be left out, if the readers will know what it is anyway - in other words, if you give the name of the composition, there is no need to say that it is a composition. In Greek, such a classifying term seems to be left out less often than in English: put the other way round, if you were translating from English into Greek, it would be quite natural to insert a classifying word in the Greek text.
The Bank of English has fifteen citations for the name of this piece. Most commonly it is preceded by the possessive form of the composer's name: Bach's X