In the beginning of the Guru Granth Sahib which contains the teachings of Guru Nanak and several other saints, Ekonkar is followed by 8 words which define Ekonkar, and then those 8 words are followed by Gurprasad. This collection of words defining Ekonkar and its path, are called the Mool Mantra.
Here are those words and the meanings of those words:
Ekonkar - one Om shape
Satnaam - true name or true identity or plainly truth
Karta Purakh - Creator, personality that creates
Nirbhau - Without fear, fearless
Nirvair - Without enmity,
Akaal Moorat - Timless shape or just timeless
Ajuni - pronounced Ajooni, Joon is cycle of birth of death, Ajooni is "one who is unaffected by the cycle of birth and death"
Saibhang - Self existing (from vedic 'svyam bhu' -- self existing)
Gur prasaad - Guru's blessing or gift (attained by Guru's blessing)