Example :  { 0, 11, 01, 011 } { 1, 01, 110 } = { 0, 11, 01, 011, 111 }

Intersection :  A string     iff    and .

Example : { 0, 11, 01, 011 } { 1, 01, 110 } = { 01 }

Complement : Usually, is the universe that a complement is taken with respect to. Thus for a language L, the complement is  L(bar) = { | }.

Example : Let L = { x | |x| is even }. Then its complement is the language { | |x| is odd }.
Similarly we can define other usual set operations on languages like relative complement, symmetric difference, etc.