A universal space is a topological space that contains a homeomorphic image of every topological space of a certain class.
A metric space 
is said to be universal for a family of metric
spaces 
if any space from 
is isometrically embeddable in 
. Fréchet (1910) proved that 
, the space of all bounded
sequences of real numbers endowed with a supremum
norm, is a universal space for the family 
of all separable metric
spaces. Holsztynski (1978) proved that there exists a metric 
on 
, inducing the usual topology,
such that every finite metric
space embeds in 
(Ovchinnikov 2000).
as a Universal Metric Space."
Not. Amer. Math. Soc. 25, A-367, 1978.Ovchinnikov, S.
"Universal Metric Spaces According to W. Holsztynski." 13 Apr 2000.