Agnitra - the protector of the fire; the keeper of the fire; he that holds the fire; Vedic Shrautin; yajna-dharma
The agnitra is a common theme in the Vedas. It is a compound term that literally means the keeper of the fire, where the fire is understood to be that present in the yajna.
Illustration (Warning: big picture, established to be online as of 2014-04-29).
Arya Dharma
A traditional name for Hinduism. Often seen with a degree of caution because it may bring unfortunate associations with the "Aryan Race" ideal as espoused by Nazi philosophy.
Aryan Invasion Theory
The Aryan Invasion Theory is a hugely controversial idea that many current Hindus feel to be both discredited and inconvenient, even dangerous. It deals with the supposed ethical and cultural origins of Indian people and, at least to a degree, of Hinduism.
Astika
In simple terms, Astika Dharma is a Hinduism proper, a Dharma that attempts to follow the teachings of the Vedas.
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Buddha Dharma - see Buddhism.
Buddhism
Buddhism is a Dharmic religion originated loosely around year 600 BC. It is usually considered Nastika Dharma by Hindus. A minority yet sometimes emphatic view insists that it is in some ways an extension of Hinduism. Syncretism with Hinduism is not unheard of, although often challenged. It is often understood that the Vajrayana schools of Tibetan Buddhism have been significantly influenced by Hinduism.
Cārvāka, also known as Charvaka and as Lokāyata, is a historically Indian system of beliefs that is generally considered to be extinct and atheistic, materialistic and skeptical in nature.
While it has on occasion been considered part of Hinduism, that is definitely a minority opinion, and possibly a complete classification error.
Please check this thread for an explanation and context of the purpose of this glossary.