It says that `func` is a type whose values are all functions with the signature `int foo(into arg)`.

The way to read a typedef (in general) is when you strip off the word "typedef", instead of declaring a type, it declares a value of that type. This applies to all types, not just function types. For example, an array of 5 ints is declared as

  int foo[5];

So the type of all 5-element arrays is defined by

  typedef int FiveLongIntArray[5];