Ma is the labial nasal, the last letter of the labial class, and with it the twenty-five stops are complete. What follows in the order are the semivowels, the sibilants and the aspirate, which the phoneticians treat as sounds of a different kind and group separately.
The letter is very common. It stands in a large number of roots, in the first person endings of the verb, in the accusative singular ending of a great many nouns and in the commonest of the pronouns, so it is among the letters a scribe writes most often. It also appears constantly in reduced form inside conjuncts.
Its place at the close of the stops is what makes the count of twenty-five a unit in the recitation rather than an arbitrary stopping point, and a learner reciting the table pauses there before beginning the second half of the consonant section.
Beyond the table, ma is the closing sound of Om in the old threefold analysis of that syllable, and the nasal mark that so many East Asian seed syllables carry represents the same nasal quality. A great many of the syllables written in Siddham on Japanese images end in it, one way or another.
The nasal mark and this letter are not the same thing, although they represent related sounds and both are commonly transliterated with an m. One is a letter of the table and the other is a mark that is not counted among the letters at all. A description of a seed syllable that confuses the two is describing something other than what is actually written.