By Baha'i Jewelry From Haifa. Bahai.com explains:

The Greatest Name
"Yá Bahá'u'l-Abhá"

". . . the symbol of the Greatest Name represents an invocation which can be translated either as 'O Glory of Glories' or 'O Glory of the All-Glorious.' The word glory used in this connection is a translation of the Arabic term Bahá, the name of Bahá'u'lláh."