Narrowest internal width

The maximum amount of information from the input that can affect the output. For example, if f(x) = SHA-1(x) || 01, and x consists of a string of 1000 binary bits, then the narrowest internal width of f(x) is 160 bits (the SHA-1 output length), and the output width of f(x) is 162 bits (the 160 bits from the SHA-1 operation, concatenated by 01).