Last month was National Stalking Awareness Month. So I learned a bit about it.
In general, stalking is defined as any unwanted attention directed toward a person or group. Women are more likely to be victims of stalking than men–and stalking is a behavioral indicator that can lead to violence.
I have friends who have been serious victims of stalking in recent months. Because of that, I have also taken some precautions of my own, learning from them.
UPDATE: Please also see the Wiki on Cyberstalking.