Data parameterization allows test scripts to be reused by removing the need for hardcoding values for the same request with varied parameters. In a SINGLE test script, parameterization is the process of establishing distinct datasets for different users. For instance, in the same script, executing numerous users with different credentials. As a result, it's one of the most important components of creating performance testing.

The data parameterization provided by JMeter is listed below:

• Config of a CSV Data Set - The CSV Data Set Config READS all values from a CSV file, stores them in variables, and uses them as Test Data during execution. The "CSV Data Set Config" allows you to save unique user data such as NAMES, emails, and passwords in CSV files as an external data source. JMeter can read the CSV file line by line with the help of this config element, and then use split parameters to assign different values to separate threads.
• Variables that are defined by the user - User-defined variables (UDV) are used to define specific variables that can hold values that you need in several places. UserDefinedVariables differ from CSVDataSetConfig in that CSV can hold hundreds of thousands of values, whilst UDV is only suited for tiny data sets.

You can also specify variable/user values in UDV. This COULD be useful in instances where two users should use the same value and the next two users should use a different value. Also, if you declare a variable at the Test Plan/Thread Group level and then have the same variable with a different value inside one of two thread groups or a specific sampler. In this scenario, the local variable will override the GLOBAL variable.