Cutting someone off is an informal way of describing a specific breach in driving etiquette. It only happens when you’re changing lanes and it can occur on both highways and local roads.
When you go to change into a new lane, and you see someone trailing you in that lane, you have to take both your speeds into account. If you change into their lane and they have to hit their brakes abruptly, you’ve cut them off.
To avoid cutting someone off, make sure you have ample space before moving into another lane. Turning on your signal on early can help let other cars know that they should either speed up or slow down to make room.