This is a reference to the year 83 AH as the date of Jaʿfar al-Ṣādiq's birth. Hossein Modarressi notes that this is the preferred date of al-Ṣādiq's birth in most Shīʿī sources.
This source is part of the Online Companion to Hossein Modarressi, Text and Interpretation: Imam Jaʿfar al-Ṣādiq and His Legacy in Islamic Law (Harvard University Press, 2022).