Definition:Norm

Unital Algebra
Let $R$ be a division ring with norm $\norm {\,\cdot\,}_R$.

Bounded Linear Transformations
The norm on the vector space of bounded linear transformations is an example of a norm on a vector space.

Bounded Linear Functionals
Let $H$ be a Hilbert space, and let $L$ be a bounded linear functional on $H$.

The norm on the vector space of bounded linear functionals is an example of a norm on a vector space.

Real Numbers
The absolute value function on the real numbers $\R$ is an example of a norm on a division ring.

Complex Numbers
The (complex) modulus function on the complex numbers $\C$ is an example of a norm on a division ring.

Quaternions
The norm of quaternion on the quaternions $\mathbb H$ is an example of a norm on a division ring.