What is logical fallacy ? 1) a mistake in thinking reasoning 2)a system of thought analysis 3) a true or false statement 4)a process of reaching conclusions

1) a mistake in thinking/reasoning. I learned this for several years, so hopefully this helps. 

Fallacy- a mistake in thinking.

A logical fallacy is a fallacy used to argue about something/a situation and it sounds to be logic due to its structure, proofs and the arguments used to persuade the other!
for instance, when you are trying to persuade that the other person's idea is not good or not useful you attack the person him/herself instead of the idea (ad hominem fallcy=