The difficulties associated with precisely defining this term (or defining it at all) are well documented.
Having been used since at least the 16th century to refer to a prowler or a poacher (Oxford English Dictionary), the term stalker started to be used by the media in the 20th century to describe people who pester and harass others, initially with specific reference to the harassment of celebrities by strangers who were described as being "obsessed". This use of the word appears to have been coined by the tabloid press in the United States.
Pathé and Mullen describe stalking as "a constellation of behaviours in which an individual inflicts upon another repeated unwanted intrusions and communications".
Stalking can be defined as the willful and repeated following, watching and/or harassing of another person. Unlike other crimes, which usually involve one act, stalking is a series of actions that occur over a period of time. Although stalking is illegal, some of the actions that can contribute to stalking are initially legal, such as gathering information, calling someone on the phone, sending gifts, emailing or instant messaging. They become illegal when they breach the legal definition of harassment e.g. an action such as sending a text is not usually illegal, but is illegal when frequently repeated to an unwilling recipient.
In fact United Kingdom law (The Protection from Harassment Act 1997) states the incident only has to happen twice when the stalker should be aware their behavior is unacceptable e.g. two phone calls to a stranger, two gifts following the victim then phoning them etc. However, the victim may feel they have been the victim of a stalking after one incident e.g. being followed home.
The Network for Surviving Stalking (NSS) defines stalking as:
Stalking’ is a range of behaviours that may seem innocent - if they’re just isolated incidents.
But when the behaviour is repeated (on more than 2 occasions) and you feel ‘fear, alarm or distress’ - take notice of these feelings. Listen to your instinct. You could be a victim of stalking and the behaviour you’re experiencing could actually be against the law.
Protection Against Stalking defines stalking as:
Stalking and harassment is behaviour that is repeated and unwanted by the victim. The behaviours may seem normal and ordinary, however, when they are repeated they can be menacing and cause alarm and distress to the victim.
For further information, please also see: