Sasaeng (사생) (also referred to as “sasaeng fan”) is a term used to describe fans who take extreme measures to get close to idols. They are known to stalk idols and try to follow their every move, among several other things. This term’s definition is further discussed in several sources, which can be found in the details below. We’ll be quoting one those descriptions, provided in a Tumblr post by user angrykpopfan:

“it basically begins with a group of people who come together. then they each take turns staking out at various places, mostly the idols’ dorms, radio recording sites, offices, etc. and when they see the idols leaving an area, they will text the others and say ‘come to (insert area here) right now, they are leaving.’ and the others, from wherever they are, get to that place as soon as they can to wait for the members. idols and managers even know some groups of sasaeng fans by face and name, and these ‘fans’ will physically try to go and hold onto the idols, swear and insult at them, touch them inappropriately, HIT and bruise the idols, and follow them around EVERYWHERE. they will knock on the manager’s vans to get them to open the window, bruise the members’ faces to leave marks, pull out their hair to ‘keep’, etc. therefore the managers must constantly protect these idols from harm and molestation, and to many korean fans, it is absolutely no wonder as to why idols and managers lose their temper with these ‘fans.’

other sasaeng fans travel through taxi. basically, the fans have to pay the taxi driver a large sum of money, and in return they follow the specific idol(s) for twenty four hours.

these fans have also been known for sending nude pictures to idols, breaking into their homes (and like one infamous incident: pee on their towels and hang them up on a rack), sending ‘gifts’ such as writing in period blood or pads drenched in period blood, etc. they have physically hurt idols, in such occasions that the managers have to beat back at the fans to protect the members. they even sell the idols’ phone numbers and social security numbers online.”