Null string

The null string (sometimes called the empty string) is the string with zero length, thus containing nothing.

The null string can be considered a null program, and in many languages it is also what is output when the null program runs. It is also used as a special value in some languages based on the string-rewriting paradigm, such as PROLAN/M.

Common ways to represent a null string include two quotes ("") or, common in academia, the epsilon character (ε) or lambda characters (λ).