Generally, stalking is one person trying to force a relationship with someone else who is not willing or not available. The term stalking was first used in connection with celebrities being stalked by obsessed fans, but stalking victims can be anyone who is being harassed, watched or followed repeatedly.
The actions that make up stalking are usually not illegal by themselves, such as calling, texting or mailing someone. But taken together and repeated to the point of harassment, they combine to make up the crime of stalking.
In some states the crime of stalking is referred to as criminal harassment or criminal menace.