Significant Harm is any Physical, Sexual, or Emotional Abuse, Neglect, accident or injury that is sufficiently serious to adversely affect progress and enjoyment of life. Harm is defined as the ill treatment or impairment of health and development. This definition was clarified in section 120 of the Adoption and Children Act 2002 (implemented on 31 January 2005) so that it may include, "for example, impairment suffered from seeing or hearing the ill treatment of another".
Suspicions or allegations that a child is suffering or likely to suffer Significant Harm may result in a Core Assessment incorporating a Section 47 Enquiry (Child Protection Enquiry).
(Definition provided by tri.x)