It was said in the beatles song "Across the Universe". Most simple translation is:

"I give thanks to Guru Dev (heavenly teacher) om"

Om is just a sound. However a more detailed translation is:

"Jai" means "O Hail" or "Victory to"
"Guru" means "Teacher"
"Deva" means "God/Lord/Demi-God"
"om" some say is the source of all existence that comes from vibration

Note Guru Dev was a Maharishi's teacher


Jai Guru Deva om definition by Urban Dictionary