What does "Return false;" in onclick event for JavaScript mean?

Question

What does "Return false;" in onclick event for JavaScript mean?

    <input 
      type="button" 
      runat="server" 
      id="btnCancel" 
      value=" Cancel " 
      style="width:70px;"
      onclick="document.location.href = 'ReportPanel.aspx'; return false;" 
    />

in the onclick event. It has return false; What does it mean? What does it mean if return true;?

Answer 1

It says "the event never happened" to the browser. If you had a submit button instead of a simple button and didn't have "return false", the form would get submitted when you click it (after executing the javascript).