Enrollment
Joining, Enlistment
noun, する verb
If you enter a group, it's called enrollment or enlistment. You're joining the group.
にゅうだん
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
入団するための申しこみ書は、細かい活字でいんさつされていました。
The application for the enrollment was printed in small type.
その教団に入団しても、何の得にもならないよ。
You won't gain anything out of joining that religious organization.
十月二十三日金曜日、Tofugu野球チームは、Tofuguオフィスで入団テストを実施します。
The Tofugu baseball team will hold tryouts at the Tofugu office on Friday, October 23rd.