SatNaam is comprised of two words "SAT" (Truth) and "NAAM" (Name). Humans have giving countless names to God that describe his characteristics eg the Almighty. But according to the Guru the original name God chose for Himself was "SAT" meaning "TRUTH".

 
kirtam naam kathay tayray jihbaa. Sat naam tayraa paraa poorbalaa.

With my tongue I describe You with the praise names.
But, the name "SAT" is Your perfect, primal one.
 
SGGS – 1082

With the blessings of the Guru, it is the one word that penetrates every heart and pierces through the Universe to take you back to the Source – Truth.
 
Five hundred years ago, when Guru Nanak Dev Ji went and met the holy men in the mountains tops, they used their supernatural powers to show off how great they were and hoped that the Guru would join them. When Nath, the head man challenged the Guru to show them a miracle too, this is all the Guru said to them:
 

"O respected Nath! Please listen to the truth that I utter.  Without SATNAAM I have no other miracle. I may wear the clothes of fire and build my house in the Himalayas . I may eat the iron and make earth move to my orders. I may expand myself so much that I could push the earth. I may weigh the earth and the sky against few grams of weight. I may have so much power that I push aside anybody just by saying so. But without SATNAAM, all these powers are momentary like the Shadow of the clouds."
 
(Bhai Gurdas Ji Var 1)

 

 
Then the holy men tried to use their Supernatural powers again but they found they had all been taken away by God. They fell at the Guru’s feet in humility and humbly asked to be blessed with the greatest gift of Naam – SatNaam.
 

"I bow before the God-Guru who announced the SATNAAM mantra."
 
(Bhai Gurdas Ji Var 1 Line 1)

 
 
 
May The One God Named Truth, the SatNaam, Bless You.