off
Switched off, not in operation. Used mainly for electrical devices and is the opposite of 'on'.
Mach bitte das Licht off, wenn du den Raum verlässt.
Please turn the light off when you leave the room.

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Switched off, not in operation. Used mainly for electrical devices and is the opposite of 'on'.
Mach bitte das Licht off, wenn du den Raum verlässt.
Please turn the light off when you leave the room.

'Off' is a loanword from English. It has become established mainly in colloquial speech for certain narrowly defined meanings.
Ist der Fernseher an oder off?
Is the TV on or off?
In the meaning 'ausgeschaltet' (switched off), 'off' is usually used with the verbs 'sein' (to be, for the state) or 'machen' (to make/turn, for the action).
Das Radio ist noch off.
The radio is still off.
The expression 'aus dem Off' (from off-screen/offstage) is a fixed technical term from film, television, and theater. It describes a voice or sound whose source you do not see in the image.
Der Film beginnt mit einer Erzählerstimme aus dem Off.
The film begins with a narrator's voice from off-screen.
The phrase 'off haben' (to have off) is colloquial and means 'frei haben' (to have time off) or 'nicht arbeiten müssen' (not to have to work). It is often used in informal conversations about work.
Ich habe am Freitag off und wir könnten ins Kino gehen.
I have Friday off, and we could go to the movies.
at / on
'an' and 'off' can both describe the state of a device. In this meaning, 'an' is the opposite of 'off': when a device is 'an', it is switched on. When it is 'off', it is switched off. 'an' is completely normal and very common in German. 'off' tends to appear in technical situations or contexts influenced by English; in everyday German, people usually say 'aus' instead of 'off'.

Nach dem Update stand der Drucker plötzlich auf off.
After the update, the printer was suddenly set to off.
Das Licht im Flur ist noch an.
The light in the hallway is still on.