1. What does it mean?
랜선집사 combines an internet connection with 집사, the affectionate pet-caretaker term. It describes enjoying an animal's photos or videos and feeling attached despite not personally caring for that pet.
Also written or said as raenseonjipsa
2. The nuance
It often concerns cats but can extend to other animals. Being a viewer is different from being the guardian; it does not grant access to the pet or its owner's private life.
3. Examples
“매일 올라오는 고양이 영상을 보다 랜선집사가 됐어.”
Watching the daily cat videos turned me into an online pet fan.
“랜선집사라 직접 만난 적은 없지만 이름은 다 알아.”
As an online admirer, I've never met them, but I know all their names.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.