noun
The branch of mathematics dealing with shapes, sizes, and properties of space.
彼は大学で幾何学を専攻している。
He is majoring in geometry at university.
この問題は幾何学の知識が必要だ。
This problem requires knowledge of geometry.
代数 is algebra, another branch of mathematics often contrasted with geometry.
From 幾何 (kika, 'how much/how many', an old term for geometry) + 学 (-gaku, 'study'). The kanji 幾何 were used phonetically for 'geo-' in the Meiji period, though the exact derivation is uncertain.