The following definition of the term nātha is given in Gorakṣa-siddhānta-samgraha:
भुवनत्रयोवैकः श्रीगोरक्ष नमोऽस्तु ते ||
Reverence to Gorakṣanāth, the Nātha, who is one in the three worlds, he as a syllable “nā” – means “nāda”, and “tha” – manifested (in the three worlds).
The other part also says that nāth is one who realises the nāda or the source of own origin. In the subtle form nāda is manifested in the form of the praṇava OM, which is known as Mahāgāyatrī, and in the gross form it is known as Brahmagāyatrī; all Navanāthas, Caurashi Siddhas, Deities, Vedas, grammar (vyākaraṇa), Purāṇa, Itihāsas, etc. are manifestations of this particular Nātha-yoga.
Indeed, practices related to nāda play a fundamental role in the Nāth Tradition.