They are flawed arguments, flaws in reasoning. Used to persuade people.
A logical fallacy is a false statement that weakens an argument by distorting an issue, drawing false conclusions, misusing evidence, or misusing language.”
There are three good reasons to avoid logical fallacies in your writing. First, logical fallacies are wrong and, simply put, dishonest if you use them knowingly. Second, they take away from the strength of your argument. Finally, the use of logical fallacies can make your readers feel that you do not consider them to be very intelligent.
Whether examining or writing arguments, make sure you detect logical fallacies that weaken arguments. Use evidence to support claims and validate information—this will make you appear credible and create trust in the minds of your audience.