That is a stupid protection measure that protects people below 18-year-old from addicting into games. When you register your account, system requires your ID number to judge if you are or older than 18-year-old. If not, you may get various of limitation when playing games. For example, if you have played 2 hours today, you may get no experience or gear after a task or kill a mob because your game time is expired (you can play 2 hours a day).

防：防止 prevent 沉迷：wallow in 系统：system

if you are younger than 18 years old, your game-time is limited. for example, you can just play some game with this system-防沉迷系统 two hours each day.