From the Oxford dictionary website:

Definition of lynch verb [with object] (of a group of people) kill (someone) for an alleged offence without a legal trial, especially by hanging

While I do realize that there are certain connotations in America as it being aimed towards African Americans, as a non American my understanding of it has always been that it is not an act aimed at a specific race. Rather a group enacting their own law without trial usually because standard legal proceedings would be viewed as a forgone failure due to lack of evidence etc. which the group would not find satisfying.