Condition
State
noun
The condition that something is in and the appearance of it is the condition / state of that object.
じょうたい
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.
妹は、精神状態が不安定であるということを私に打ち明けた。
My little sister told me about her unstable state of mind.