a particular area of knowledge or the process of becoming an expert in a particular area专门化,专业化;专业范畴
Specialization (= limiting study or work to one particular area) usually doesn't occur until PhD level.专门化通常到博士阶段才发生。
The lawyer said that he was unable to help us because our case fell outside his specialization.律师说他帮不了我们,因为我们的案子超出了他的专业范围。