Flawless is an adjective that means "without any imperfections," like your flawless vocal performance — not one mistake. That's why the choir teacher gave you an A+.
In flawless you can see the word flaw, which means "a fault." So something that is flawless is free of faults, perfect. If you've never gotten in any kind of trouble, your record is flawless. Antique car collectors look for that flawless model — no dents, dings, or signs that anyone had even sat in it.