The prefix Abhi is used in the sense of preponderant, great, excellent, sublime, distinct, etc. Indeed, it is a Manual compiled for easy learning of the Abhidhamma Pitaka.
According to Bhikkhu Bodhi, the Abhidhammattha-sangaha is one of the most important texts in the Theravada tradition. Bhikkhu Boddhi writes:
In nine short chapters occupying about fifty pages in print, the author provides a masterly summary of that abstruse body of Buddhist doctrine called the Abhidhamma. Such is his skill in capturing the essentials of that system, and in arranging them in a format suitable for easy comprehension, that his work has become the standard primer for Abhidhamma studies throughout the Theravada Buddhist countries of South and Southeast Asia. In these countries, particularly in Burma where the study of Abhidhamma is pursued most assiduously, the Abhidhammattha Sangaha is regarded as the indispensable key to unlock this great treasure-store of Buddhist wisdom.[2]
Regarding the author of the text, Bhikkhu Bodhi explains:
This work is ascribed to Acariya Anuruddha, a Buddhist savant about whom so little is known that even his country of origin and the exact century in which he lived remain in question.