Four Immeasurables, Loving Kindness Part 3

The middle part of the first immeasurable has this section, bde ba is happiness, also sometimes bliss, but in this specific case it is translated as happiness. In tantric texts this would most likely be bliss. It could even be shortened to bde.

In Sanskrit this is sukha, as in Sukhavati, realm of bliss, in Tibetan bde ba can -- the place that contains bliss. The tantric form is the mahasukha, great bliss. Sukhavati is the pure realm of Amitabha, arealm where a practitioner could take rebirth during bardo through a combination of pure faith, merit, and single-pointed determination to get there.

dang is the binding particle, binding to bde ba'i rgyu. rgyu is cause or causes, and there's a genitive particle between bde ba and rgyu, the 'i letter, so when you combine this from right to left it is the causes of happiness. rgyu is another of those words good to learn, as it's used to define causes of all kinds.