Y stands for Yogi,
Maharishi Mahesh Yogi, (Yogi means great Seer) was a great Seer and travelled the world teaching Transendental meditation.
'Transendental meditation'.....has been described as both religious and non-religious and mainly rooted in Hinduism. The meditation practice involves the use of a Mantra (especially in Buddhism and Hinduism). It is a word or sound that is believed to have a special spiritual power.
A personal Mantra is sometimes repeated as an aid to meditation or prayer.
Association with the Beatles.
The Beatles went to study with him in Bangor North Wales, before travelling to Rishikesh in India (1968) to devote themselves fully to his instructions.
Ringo Starr and his wife Maureen left after ten days, Paul and his girlfriend Jane Asher left after five weeks and John and Cynthia Lennon, George Harrison and Patti Boyd, left sixteen days later . During their stay they were led to believe that the Marahishi Yogi had made unwanted advances to the actress Mia Farrow it is widely believed that instigated their return home, In 1968 the Beatles renounced their association with him.