A misconception resulting from flaw in reasoning, or a trick or illusion in thoughts that often succeeds in obfuscating facts/truth.
A formal fallacy is defined as an error that can be seen within the argument's form. Every formal fallacy is a non sequitur (or, an argument where the conclusion does not follow from the premise.)
An informal fallacy refers to an argument whose proposed conclusion is not supported by the premises. This creates an unpersuasive or unsatisfying conclusion.
A few books to help you get a real handle on logical fallacies.