The science of exegesis and interpretation is a very complex one and so, there are so many definitions available for it.
According to "Amin al-Islam Tabarsi" exegesis and interpretation is unveiling the obscure words. In other words it is uncovering the verses of the Holy Quran and their purposes.
On different occasions, Imam interpreted the Holy Quran verses and these interpretations have been compiled in five volumes.
This exegesis of the Quranic verses by Imam contains so many niceties and nuances of interpretation.
Imam's Exegesis (Tafsir) of the verses of the Holy Quran can be traced in his works like, "Adab-o-Salah", "Sahifah i-Imam", "Kashf al-Asrar", "Sharh i-Dua i-Sahar", "Sharh i-Chehel Hadith", etc.