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general idea; concept; notion
この哲学書は難解な概念が多くて読みづらい。
This philosophy book is hard to read due to many difficult concepts.
時間という概念は文化によって異なる場合がある。
The concept of time can differ depending on culture.
子供に抽象的な概念を教えるのは難しい。
Teaching abstract concepts to children is difficult.