Is delaying Maghrib prayer to perform it half an hour before the 'Isha call to prayer considered a delayed combination (jam' ta'khir)? And what is a delayed combination, with an example?

"Jam' Al-Ta'kheer" (delayed combining of prayers) is the act of delaying the Maghrib prayer until the time of Isha, or the Dhuhr prayer until the time of Asr. The majority of jurists do not permit combining prayers except in specific circumstances. The questioner should pray in school before the time for Maghrib expires, as Allah Almighty says: "Indeed, prayer has been decreed upon the believers a book [to be observed at] fixed times." Delaying a prayer beyond its prescribed time without a valid excuse is forbidden, even if she reaches home before the Isha adhan. However, a group of scholars has permitted combining prayers without an excuse, provided that it is not made a habit.