Alternatively, the DfE has described bullying more succinctly as: "Behaviour by an individual or group, repeated over time, that intentionally hurts another individual or group either physically or emotionally."
Some subtle differences between these definitions and the US definition are worthy of consideration. For example, the US definition is from the perspective of the victim - "unwanted, aggressive behaviour" - whereas those used in the UK are from the perspective of the perpetrator - "intention to harm". And whereas the US definition includes isolated incidents that have the potential to be repeated, UK definitions infer that single incidents are not bullying.
Look to other countries and you will find further differences. Take, for example, the definition used by Professor Dan Olweus in his national study of Norwegian schoolchildren: "We say a young person is being bullied, or picked on, when another young person, or a group of young people, say nasty and unpleasant things to him or her. It is also bullying when a young person is hit, kicked or threatened, locked inside a room, sent nasty notes, when no one ever talks to them and things like that. These things can happen frequently and it is difficult for the young person being bullied to defend himself or herself. It is also bullying when a child or young person is teased repeatedly in a nasty way. But it is not bullying when two young people of about the same strength have the odd fight or quarrel."
Here, Olweus attempts to separate occasional incidents from more concerted campaigns of abuse.
So, how should we define bullying practically in a school if, even on a government level, with experts at hand, universal agreement cannot be reached? Schools have to work through the three key issues and agree for themselves the definition they will work to.
First, whose perspective do we take? In UK law, the perspective of the victim is often taken. For example, in the Protection from Harassment Act 1997, if an individual believes that they have been harassed and a reasonable person furnished with the same information also believes that the behaviour constitutes harassment, then, to all intents and purposes, it is harassment, regardless of the perpetrator's intentions. Thus, it seems appropriate to take the perspective of the victim for bullying.
However, a caveat should be added here. US educators acknowledge that in some cases, where a perpetrator has special educational needs, it is important to establish whether or not they understand that their behaviour was wrong. If they do not, any sanction should be revised accordingly and should include an element of social skills training.
Second, how do we classify and record single incidents? If we take a preventative approach, rather than waiting for a pattern of abuse to emerge, then addressing a single incident becomes an index of best practice. That does not mean, however, that a teacher may wish to describe single incidents as bullying.
Finally, how do we assess an imbalance of power? It is perhaps easier when there are clear differences in size or physical strength between perpetrator and victim. But much of the bullying that takes place occurs within classes and year groups and, as I noted earlier, imbalances of power may not be observable. Taking the perspective of the victim may be helpful here. Asking whether they felt able to stand up to the aggressor seems a useful marker of that imbalance.
Ultimately, a clear definition of bullying and a statement about how that definition is interpreted when judging students' behaviour are pivotal to any anti-bullying policy or intervention. It may be difficult, but if agreement can be reached on the three key areas noted here then a workable definition can be formulated. It is just up to teachers to enforce it.
Ian Rivers is professor of human development at Brunel University, England, and a visiting professor in the Faculty of Health, Social Care and Education at Anglia Ruskin University