Meaning in this text
The four cosmic time cycles that repeat in a vast sequence: Satya Yuga (age of truth, 1.728 million years), Treta Yuga, Dvapara Yuga, and Kali Yuga (the shortest, darkest age, currently underway). The Bhagavatam teaches that in Kali Yuga, the chanting of God's names is the most effective spiritual practice.
On this site, Yuga is treated as a reading aid rather than a final doctrinal definition: use it to move from a question about a term into the chapters where the term actually appears.