Literally the word means a ‘reflection,’ an ‘appearance,’ hence, a false phenomenon which shows itself as the real. For instance, the reflection of an object in a mirror is an ‘ābhāsa.’ The word is widely used in Advaita Vedānta in the context of the relationship between the jīva (individual self) and Brahman (the Supreme Self). The jīva according to one of the schools of Advaita Vedānta, is only an ‘ābhāsa’ of Brahman in and through the medium of the antaḥkaraṇa (mind).
In Hindu logic, the word is used with regard to hetu or cause. Owing to several factors, a real hetu can get obscured and a false hetu, hetvābhāsa, can appear in its place leading to wrong conclusions. For more details see HETVĀBHĀSA.
In temple architecture, the word stands for a particular type of vimāna (tower over the sanctum sanctorum).