Gha is the fourth consonant of the varnamala, the voiced aspirated velar and the fourth member of the first varga. The voiced aspirates are the sounds of Sanskrit that speakers of European languages find hardest to make, because the aspiration is voiced throughout rather than following the release as a puff of breath; phoneticians describe them as breathy voiced or murmured, produced with the vocal folds held in a configuration that lets air escape while they vibrate. There are four of them among the stops, one in each varga except that every varga has one, so five in all, and they occupy the fourth slot in each class. Their presence in the table is not a refinement added by grammarians looking for symmetry.
Sanskrit inherited the series from the ancestor language it shares with Greek, Latin, the Germanic and Slavonic languages and the rest, and it kept the series where most of the relatives lost or transformed it. That retention is one of the reasons Sanskrit mattered so much to the comparative philology of the nineteenth century, and it is why Whitney's grammar, written inside that tradition, is careful about how these sounds are described. Devanagari gives each aspirate a letter of its own rather than writing a stop followed by a breath sign, which is why the consonant table runs to thirty-three signs rather than to a shorter set with a modifier attached. That treatment is inherited from Brahmi, and it is one of the structural differences between the Indian scripts and the Semitic ones, which mark aspiration, where they mark it at all, with a separate stroke or a dot.