An object of the class cpp0x::tuple<...> represents a heterogeneous tuple of elements of the types specified in parameters, which are in variadic number.
There is actually no class in namespace CGAL::cpp0x with this name, but a using declaration which imports a class from another namespace. By order of priority: the one in namespace std is used (provided by C++0x), if not found, then the one in namespace std::tr1 is used (provided by TR1), and finally, the fallback solution is taken from Boost.
The parameters ... are the value types.
Some free functions part of the standard interface of tuple are also brought in namespace CGAL::cpp0x with using declarations. These are make_tuple, get and tie.