world of ideas; intellectual circles
Refers to the realm of thought, philosophy, or the intellectual community. Often used in discussions of academic or ideological trends.
He had a great influence on the world of ideas.
In the intellectual circles of that time, that theory was mainstream.
言論界 focuses on the world of public discourse and journalism, whereas 思想界 emphasizes philosophical and ideological thought.
Compound of 思想 (thought, ideology) and 界 (world, sphere). The exact historical derivation is uncertain, but the word follows a common pattern for naming intellectual domains.