The technical definition of harassment is “the act of systematic and/or continued, unwanted and annoying actions of one party or a group, including threats and demands”. Basically, if someone is bothering you again and again, including threats and demands, you can report it as harassment.
The main types of anti-social behaviour in this category are:
Hate incidents where the abuse involves your race, religion, gender, sexual orientation, age or disability
Violence or the threat of violence to another person
Malicious phone calls, texts and emails
Hoax calls to the emergency services or other third parties
Animals not properly restrained in public places
Stalking, mentioned above and defined as unwanted or obsessive attention by an individual or group, is covered in more detail by the National Stalking Helpline and therefore the information is not repeated here. See http://asbhelp.co.uk/emily-maitlis-opens-up-about-being-victim-of-stalker/ and http://asbhelp.co.uk/stalking-not-taken-seriously/ for our case studies about victims of stalking.
Bullying, including cyber-bullying, is also a form of harassment. See the excellent work of the Anti-Bullying Alliance (http://www.anti-bullyingalliance.org.uk) if you are a victim of bullying.
If you feel like you are being targeted because of who you are, this may be a Hate Incident or Hate Crime. It is definitely worth emphasising this to the Police because it will be treated with a higher level of seriousness. For more information on Hate Crime see here.
For a victim's experience of the challenges of defining harassment see this case study.
For a printer-friendly version of this information see here: Harassment