不安（ふあん） means anxiety, unease, or insecurity.
Use it for a vague inner feeling that something is not safe, stable, or certain. It often comes up when you feel unsure about the future, lack confidence, or sense that something may go wrong.
Do not confuse it with 心配（しんぱい）.
不安 focuses on the feeling of unease itself.
心配 focuses on worry about a specific person, thing, or situation.
不安 can be used as both a noun and a な-adjective:
不安です = feel anxious / feel uneasy
不安な気持ち（ふあんなきもち） = an anxious feeling
将来が不安（しょうらいがふあん） = anxiety about the future