1. What does it mean?
즐겜 abbreviates 즐거운 게임. It can be a friendly wish to enjoy a game or a description of a relaxed approach focused on fun. 즐겜러 is someone who plays that way.
Also written or said as jeulgem
2. The nuance
Relaxed play is not the same as deliberately ruining teammates' games. Expectations differ between a casual session and a competitive queue, so context matters.
3. Examples
“오늘은 점수 신경 안 쓰고 즐겜하자.”
Let's enjoy the game today without worrying about points.
“친구들이랑 웃으면서 하니까 진짜 즐겜이었어.”
Playing and laughing with my friends made it a genuinely fun session.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.