noun
Western history; history of the Western world
Refers to the academic field or subject of Western history, often contrasted with 東洋史 (Eastern/Asian history).
大学で西洋史を専攻しています。
I'm majoring in Western history at university.
世界史 is world history, a broader category that includes both Western and Eastern history.
Compound of 西洋 (せいよう, 'the West') and 史 (し, 'history').