For the exact definition:
Section 4.4 of the Java Language Specification describes type variables. You can use type variables in generic class, interface, method and constructor declarations as parameters in those declarations - so there they are called type
parameters.
When you use a generic class or interface with a specific type, in other words when you fill in specific, existing types for the type arguments, you get a
parameterized type. For example,
List<String> is a parameterized type - you've filled in
String for the type parameter
T of the generic type
List<T>. The Java Language Specification calls the type that you fill the parameter with the
actual type argument.
The words "parameter" and "argument" mean the same (so "type parameter" and "type argument" also mean the same).