Instance
The size of an instance x denote by |x|.
The number of bit needed to represent the instance on a computer.
Often used the word “size” to mean any integer that in some way
measures the number of components in an instance.
For example
when talk about sorting an instance involving n items is
generally considered to be of size n.
When talk about numerical problem sometime give the
efficiency of algorithms in terms of the value of the instance,
which is the number of bits needed to represent this value in
binary.