Refers to the act or incident of having property stolen. Often used in compounds like 盗難事件 (theft case) or 盗難防止 (theft prevention).
There was a theft at the store last night.
盗難防止のために鍵を二重にかける。
I double-lock the door to prevent theft.
My bicycle was stolen from the parking area.
This lock is installed to prevent theft.
I filed a theft report with the police after my wallet was taken.
A theft incident occurred in this area last week.
盗難 describes the incident of having something stolen from a victim's perspective, while 盗用 describes the act of misusing something without authorization.
certificate of theft; theft certificate
identity theft