A telling-off is the act of speaking angrily to someone because they have done something wrong. It is a countable noun, and it lives almost entirely in the phrase "give someone a telling-off" or "get a telling-off": a teacher gives a child one, a boss gives a worker one. The scale matters. A telling-off is words only — no punishment, no consequences beyond the scolding — and it is usually over in a minute. It is British English, and it is warm and informal; the speaker is often smiling a little, even when reporting something unpleasant. Because of that, adults often use it about themselves half-jokingly: "I got a right telling-off from my wife." Americans would say "a talking-to" or "a scolding". You will also see it without the hyphen, as telling off. The plural is tellings-off, though most people avoid it because it sounds odd.