Wikipedia
Quasinorm
In linear algebra, functional analysis and related areas of mathematics, a quasinorm is similar to a norm in that it satisfies the norm axioms, except that the triangle inequality is replaced by
∥x + y∥ ≤ K(∥x∥ + ∥y∥)
for some K > 1.
This is not to be confused with a seminorm or pseudonorm, where the norm axioms are satisfied except for positive definiteness.