Entrance, Imprisonment, Internment
noun, verbal noun
You enter a place. So, you have been given (or forced) admission into this place. You have been given entrance. For example, "admission" into a prison is something you could gain by not doing your WaniKani reviews in certain Crabigator ruled countries.
入所 refers to the act of entering facilities or institutions, commonly those with names ending in 所, such as 研究所 (research institutes).
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.
My grandma joined the group home in March.
I had an entrance test for a model agency today.
Be sure to check the rules before your admission.