What is the difference between User Parameter, User Defined Variable and CSV Data Set Config?

User Parameter is a preprocessor whereas CSV Data Set Config and User Defined Variables are Config Elements.
In User Defined Variables, there is only one value of the variable can be defined whereas, in User Parameters and CSV Data Set Config, multiple values can be defined for a variable.
Test Data cannot be added via an external file in User Parameters and User Defined Variables whereas CSV Data Set Config use .csv file format as a test data.
Since there is only one value can be given in User Variables so bulk test data can not be used. The bulk test data can be added manually in User Parameters, but it is time-consuming. Although the primary purpose of CSV Data Set Config is to access an external file so that bulk test data can be available for the test.