What makes the execution a lynching is the nature of it being done without a court trial by people who believe the accused is guilty of a crime.
Lynchings have been used in the southern states of the United States of America against African Americans during the time of slavery but more commonly after the abolition of slavery during the time of civil rights activism and the times of the various Ku Klux Klans.
Lynching is both an illegal and horrible practice that took the lives of many innocent people who never got a chance of fair trial. Another unjust thing about lynching is that the murderers were almost never prosecuted.
Lynching Facts for Kids. Kiddle Encyclopedia.