Unary coding is an entropy encoding that represents a Natural number, n, with n-1 ones followed by a zero. For example 5 is represented as 11110. Some representations use n ones followed by a zero. Also the use of ones & zeros are interchangeable without loss of generality.
Unary coding is an optimally efficient encoding for the following discrete probability distribution:
For n=1,2,3,...
A modified unary encoding is used in UTF-8.