Adi is a Hindu, Buddhist, and Theosophical term meaning the first part of reality. It has to do with the first cause or even Adi-Ananta

Causeless cause

Causeless Cause, a.k.a Uncaused Cause or All-Cause is a term in Theosophical Philosophy for 'An Omnipresent, Eternal, Boundless, and Immutable Principle...' also described as 'infinity' to 'intelligence' & 'spirit' & 'consciousness' & 'essence' to 'the one...

--at least as unity of infinity (as Plotinus and others say) emanating the first finite one. This is called Brahm (in Hinduism) and Adi-Buddha

Adi-Buddha

In Vajrayana Buddhism, the Adi-Buddha, or Adibuddha , is the "Primordial Buddha." The term refers to a self-emanating, self-originating Buddha, present before anything else existed. Samantabhadra, Samantabhadri and Vajradhara are the best known names for Adi-Buddha, though there are others...

, and Theosophy also says it has to do with the Divine

Divinity

Divinity and divine are broadly applied but loosely defined terms, used variously within different faiths and belief systems — and even by different individuals within a given faith — to refer to some transcendent or transcendental power or deity, or its attributes or manifestations in...

 Monad

Monad

-Philosophy:*Monad a term meaning "unit" used variously by ancient philosophers from the Pythagoreans to Plato, Aristotle, and Plotinus to signify a variety of entities from a genus to God....

, e.g. Logos

Logos

' is an important term in philosophy, psychology, rhetoric and religion. Originally a word meaning "a ground", "a plea", "an opinion", "an expectation", "word," "speech," "account," "reason," it became a technical term in philosophy, beginning with Heraclitus ' is an important term in...

.