In Jainism, Aum is regarded to be a condensed form of reference to the Five Parmeshthis, by their initials A+A+A+U+M (o3m). The Dravyasamgrah quotes a Prakrit line:
ओम एकाक्षर पञ्चपरमेष्ठिनामादिपम् तत्कथमिति चेत “
अरिहंता असरीरा आयरिया तह उवज्झाया मुणियां
“oma ekākṣara pañca-parameṣṭhi-nāmā-dipam tatkabhamiti ceta “
arihatā asarīrā āyariyā taha uvajjhāyā muṇiyā”
“Aum” is one syllable made from the initials of the Panch Parameshthis. It has been said: “Arihanta, Ashiri, Acharya, Upadhyaya, Muni”.
In Short, ‘a’ + ‘a’ + ‘ā’ + ‘u’ + ‘m’ = aum
a = Arihanta
a = Asrira (Siddha)
ā = Acharya
u = Upadhyaya
m = Muni (Sadhu)
Thus, ओं नमः (om namah) is a short form of the Navkar Mantra.