This is the 98th most frequent Japanese word.
世界
"World" or "Society."
In this instance, '世界' refers to an imagined or fictional realm, illustrating its use in creative or fantastical contexts.
ファンタジー世界の物語が好きです。
I like stories set in fantasy worlds.
In this sentence, '世界' (sekai) means 'world' as in the entire globe or the earth, referring to the planet and its natural beauty.
この世界は美しいです。
This world is beautiful.
Here, '世界' is used to denote a particular domain or field of study, specifically the field of biology in this context.