Sutra or dharani?
The Sanskrit word Sutra is usually interpreted as deriving from the root siv meaning "to sew" and as referring to a "thread" that holds things together, like the English word suture. However some scholars have suggested that it might instead come from sukta, meaning “wise saying. Whatever its derivation, sutra was used . . . to denote a scripture.
According to traditional accounts Buddhist sutras date back to the First Council, which was held . . . immediately after the Buddha's Nirvana in 383 B.C. Many scholars now believe such an account was a later fabrication by early Buddhist sects anxious to authenticate their selections and interpretations of the Buddha's teachings. . . . These early sects also began to apply the word sutra not only to discourses of the Buddha but also to discourses on the Abhidharma. As time went on, however, the word shastra, meaning "investigation," was used for Abhidharma texts, and the word sutra was reserved for sermons of the Buddha or disciples empowered by him to speak on his behalf.
The first translation of the Heart Sutra was titled the Prajna-paramita Dharani. . . The Heart Sutra was not considered a "sutra" until Hsuan-tsang's translation of 649. Prior to that, the text was considered a mantra or dharani, as reflected in the earlier translations of the title . . . Also, it is worth noting that none of our extant Sanskrit copies includes the word sutra in the title.
Mantras and dharanis
At some point in time the term dharani came to be used for meaningful, intelligible phrases, and the term mantra for syllabic formulae which are not meant to be understood. The "Heart Sutra" contains a mantra. In fact, in the earlier, shorter version of the Heart Sutra, the mantra is the conclusion. If the earlier versions were not even named "sutra," was the Heart Sutra originally a dharani ending with a mantra?
Often a distinction is made between mantras and dharanis, whereby mantras are said to be strings of one or more syllables not meant to be understood as human language, and dharanis are said to be intelligible summaries of some profound truth. But this is a late distinction, and early texts use the words mantra and dharani in reference to both intelligible and unintelligible incantations. Since this sutra uses the word mantra, and the sutra itself was often referred to as a dharani, it was most likely composed before such a distinction was made.
Andre Padoux says, "a mantra has a use rather than a meaning" . This mantra, however, has both. It contains the essential teaching of the Prajnaparamita and also enables those who chant it to join the lineage of buddhas who who have their origin in his teaching. In his commentary, Vajrapani says,"The mantra of the Perfection of Wisdom is not a mantra for pacification, increase, power, or wrath What is it?? By merely understanding the meaning of this mantra, the mind is freed"