Lynching in common usage means hanging of someone by a mob. In the past, criminals were hanged by the community, rather than waiting for the law to make up its mind. This was a classic theme of old TV westerns, and overstated to some extent in folklore, but it did happen regularly as a form of mob justice. A 'lynch mob' in metaphoric modern usage is a group of angry people. In US slang, it's sometimes called a 'necktie party'. It was also used by some groups as a means of persecution of minorities. Lynching is classed as murder, in modern law.