This is the 4765th most frequent Russian word.
занятиях
"Lessons" or "activities."
The word "занятиях" refers to scheduled lessons or academic activities, in this case, a mathematics class.
Сегодня я был на занятиях по математике.
Today, I attended math classes.
Here, "занятиях" reflects a series of educational sessions focused on programming.
На этих занятиях мы изучаем основы программирования.
In these classes, we study the basics of programming.
The word "занятиях" denotes the scheduled educational sessions that were missed.