Without permission; without notice — doing something without asking or informing others.
無断で入らないでください。
Please do not enter without permission.
写真を無断で使うのは著作権侵害になる。
Using photos without permission can constitute copyright infringement.
彼は無断で休暇を取ったので上司に叱られた。
He took time off without permission and was scolded by his boss.