In this section, we define some important terms that are used th=
roughout this guide. In particular, *subset*, *value set*&nbs=
p;and *reference set*.

*Subset* and *value set* are gene=
ral terms that are not specific to SNOMED CT. However, it is impo=
rtant to understand what they mean, and how they relate to SNOMED CT *re=
ference sets*.

In summary:

- A sub=
set is a set of members
~~all of which~~are members of= another set (from*se= t theory*in mathematics). - A value set is a uniquely identifiable=
set of valid concept representations, where any concept representation can=
be tested to determine whether or not it is a member of the
*value set*.<= /span> - A reference set is a standard =
format for maintaining and distributing a set of references to SNOMED=
CT components.=20
=20 =20

In the following subs= ections, we describe each of these terms in more detail.