In linguistics, a zero or null is a segment which is not pronounced or written.
It is a useful concept in analysis, indicating lack of an element where one might be expected.
It is usually written with the symbol "∅", in Unicode U+2205 ∅ EMPTY SET (∅, ∅, ∅, ∅).
A common ad hoc solution is to use the Scandinavian capital letter Ø instead.
There are several kinds of zero: