1A sphere, globe, or ball-shaped object; this reading (きゅう) is typically used in more formal, technical, or scientific contexts (an everyday physical ball is usually read たま).
地球はほぼ球の形をしている。
The Earth is nearly spherical in shape.
地球儀は、地球を小さな球で表した模型だ。
A globe is a model that represents the Earth as a small sphere.
満月の夜、月がまるで完全な球のように見えた。
On the night of the full moon, the moon looked like a perfect sphere.
2In mathematics: a ball or sphere — the three-dimensional solid (ball) or the surface (sphere) in geometry.
半径 r の球の体積は (4/3)πr³ である。
The volume of a sphere with radius r is (4/3)πr³.
この問題は球の表面積を求める問題だ。
This problem asks to find the surface area of a sphere.
3A counter for pitches in baseball (used as ～球, e.g. 'three pitches').
彼のストレートはすでに3球目だ。
His fastball is already the third pitch.
あと一球で試合が決まる。
One more pitch will decide the game.