Consider a inner product space \( V \). A subset \( S \subseteq V \) is called an orthonormal system if and only if for all \( e, f \in S \):

1. \( \|e\| = 1 \),
2. if \(e\neq f\) then \(e\) and \(f\) are orthogonal .

See also Link to heading

• orthonormal frame
• orthonormal basis