When you're distracted, something else has your attention, making you lose focus or become nervous.
If a dog keeps barking or a car alarm won't stop going off, it's easy to become distracted: annoyed and not very focused on what you're trying to do. We also say people are distracted when they're worried about something. If you think you might lose your job, you'll be distracted by thinking about it. Knowing a family member has a disease can make you distracted with worries. When you're distracted, your mind is somewhere else.