Meaning: Two-dimensional world.
Chinese people use the expression: “二次元世界” (èrcìyuánshíjiè) to specify the two-dimension world of Manga, Anime, cartoons, tv-series, animation and video-games.
During the 80’s and 90’s Chinese children could finally access to all the Japanese sub-culture of anime and manga. They sat down in front of a TV or a book and started to live in another world, a two-dimensional world made of fantasy, creativity, imagination.
Need to know: “二次元” has a good connotation and it’s usually used when people like the 2D world, on the contrary “贰刺螈”（èrcīyuán) is used when the speaker wants to ridicule, to mock this world.
Related words: 2.5次元, 三次元, 弹幕
In Use: world of: “谁能告诉我进入到二次元的方法？” ( Who can tell me how to start with the “two-dimensional world”?)
genre: “XX是一曲很棒的二次元音乐。” ( XX is a really cool two-dimensional song)
Interesting things: 2.5次元 is a 2.5-dimensional world, the one of cosplays!