届 (jiè) is a measure word for cycles, classes, or sessions of something held on a regular schedule — Olympic Games (
本届奥运会 'this Olympics'), graduating classes (2024
届 'class of 2024'), elections, conferences.
上届 = 'last cycle',
本届 = 'this cycle',
下届 = 'next cycle'. Don't confuse with
上次 (last time, generic) or
上个 (the previous one).