In mathematics

The quaternions form a number system that extends the complex numbers.

• Quaternion rotation
• Quaternion group, a non-abelian group of order 8

Symbols

• Imperial quaternions (heraldry of the Holy Roman Empire)
  • Quaternion Eagle

Military uses

• A group of four soldiers in the Roman legion
• A fireteam

Other

• Quaternion (gathering), four folded sheets as a unit in bookbinding
• Quaternion (poetry), a style of poetry with four parts