Terminology

Type parameter and type argument

Declaration of type variables are called type parameters and the concrete values passed into them are referred to as type arguments.

class Optional<T> { // T: type parameter
}

class Container {
  // String is the type argument
  private Optional<String> stringOpt;
}

Source: https://docs.oracle.com/javase/tutorial/java/generics/types.html

Nested classes vs. inner classes

A nested, non-static class is called an inner class. If it is static it's simply called static nested class.

class Container {
  class InnerClass {
  }

  static class StaticNestedClass {
  }
}

Source: https://docs.oracle.com/javase/tutorial/java/javaOO/nested.html