The core concept is understanding synonyms. Synonyms share similar meanings but often have different nuances or usages depending on the context. Option B correctly captures this essence, while options A, C, and D are incorrect. Option A is too absolute, as synonyms rarely if ever have exactly the same meaning in all contexts. Option C is the definition of antonyms, and option D misrepresents the relationship between synonyms. The correct answer is B because it recognizes that while synonyms are similar in meaning, they may not be completely interchangeable.