Impeccable means absolutely perfect, without any flaws or mistakes. When something is impeccable, you can't find anything wrong with it, no matter how carefully you look.

When a pianist gives an impeccable performance, every note rings out exactly right. When someone has impeccable manners, they always know the right thing to say and do. A detective with impeccable attention to detail notices every tiny clue that others might miss.

You'll often hear about someone's impeccable taste in clothes, meaning they always look put-together and stylish, or impeccable timing, meaning they do things at exactly the right moment. A student might turn in homework with impeccable handwriting: neat, clear, and beautiful.

Impeccable sets an extremely high standard. Your work might be good, or even excellent, but impeccable means it couldn't be better. That's why the word carries such weight when someone uses it. When your teacher says your essay was impeccable, that's serious praise. It means every part of it was done exactly right.