Ad Hominem is one of the most well known logical fallacies. Ad Hominem translates as ‘to the man’ - this refers to attacking the person making the argument rather than the argument itself.
An example of the an ad hominem attack would be ‘Jordan Peterson is a dickhead and therefore he’s wrong’ Jordan Peterson’s dickheadness has no bearing on whether he is right or wrong.
People often conflate an insult with an ad hominem attack. ‘Jordan Peterson is wrong to think that the nuclear family is the best way to raise a child, many people have succeeded from non-traditional family units. Jordan Peterson is also a dickhead’ that’s a refutation followed by an insult, it’s not an ad hominem attack.