A flaw is a problem or err or (small or large) that makes something less effective or valuable. The word flaw can be used for problems in objects, ideas, or people's character:

Objects: This diamond is less expensive because it contains several flaws.

Ideas: There's a major flaw in your plan - it will never work.

People: He's the perfect boyfriend; his only flaw is the fact that he sometimes speaks without thinking.

The word defect also refers to a problem, usually when a mechanical or manufactured item was produced with the problem. We often use the adjective

defective.

Defects in the machinery caused several fires to break out in the factory.

This camera is defective - the flash doesn't work. I'll need to exchange it.

When a baby is born having something wrong or not normal with its body, this is called a birth defect.

The word fault refers to responsibility for a problem or mistake. It's usually used with "my/your/his/her fault" or to say that a person/company is "at fault" for the problem.

The car accident was his fault because he drove through a red light.

The giant factory is at fault for the air pollution in this area.

You can also use the word faults to talk about problems with people's character in general, as in the expression, "Everyone has their faults."

Fact
During the baseball rivalries between the two major leagues in the 1890s, the Pittsburgh Nationals took advantage of a technicality and signed a player away from another club. The Nationals' president, J. Palmer O'Neill, was called J. Pirate O'Neill, and his club became the Pittsburgh Pirates.      .. More >>