Why can lambdas convert function calls into Actions?

In this code fragment:

List<String> names = new List<String>();
names.Add("Bruce");
names.Add("Tom");
names.Add("Tim");
names.Add("Richard");

names.ForEach(x => Print(x));

private static string Print(string s)
{
    Console.WriteLine(s);
    return s;
}

Print is not an Action for sure since it is returning string; however x=> Print(x) is, why?