1.NounA set A such that every element of A is also an element of S."The set of integers is a subset of the set of real numbers.; The set
{
a
,
b
}
{\displaystyle \lbrace a,b\rbrace }
is a both a subset and a proper subset of
{
a
,
b
,
c
}
{\displaystyle \lbrace a,b,c\rbrace }
while the set
{
a
,
b
,
c
}
{\displaystyle \lbrace a,b,c\rbrace }
is a subset of
{
a
,
b
,
c
}
{\displaystyle \lbrace a,b,c\rbrace }
but not a proper subset of
{
a
,
b
,
c
}
{\displaystyle \lbrace a,b,c\rbrace }
."