• 世界せかい — the world
• 限界げんかい — limit; boundary
• 業界ぎょうかい — industry; business world
• 政界せいかい — political world
• 学界がっかい — academic circles
• 視界しかい — field of vision; visibility
• 世界中せかいじゅう — all over the world

界 combines the element 田 (rice field) with 介 (to intervene), evoking boundaries between fields. By extension, it came to mean broader “spheres” or “realms,” such as the world (世界) or professional fields (業界).

世界せかいには たくさんの 文化ぶんかが あります。
There are many cultures in the world.

限界げんかいを 超こえる 努力どりょくが 必要ひつようです。
You need effort to go beyond your limits.