interruption
A break or stop in something that is happening.
An interruption is a disruption to something that's not finished. If your teacher is explaining fractions and a fire drill suddenly rings, that alarm is an interruption. If you start answering a question before your friend finishes asking it, you're interrupting them.
Interruptions can be accidental or intentional. Sometimes they're necessary: a parent might interrupt a child who's about to touch a hot stove. Other times they're just rude: cutting someone off mid-sentence because you think what you have to say is more important shows poor manners and disrespect.
Some interruptions last seconds, like when a phone buzzes during homework. Others last much longer: if a snowstorm causes a week-long interruption in mail delivery, letters simply stop coming until the weather clears. Scientists might study an interruption in someone's sleep patterns. A construction project might face frequent interruptions due to bad weather or supply problems.
The word carries a sense of breaking continuity or flow. When something proceeds without interruption, it continues smoothly from start to finish. Learning to speak without interrupting others, and to handle interruptions patiently when they happen to you, are both signs of maturity.