QuickTest Professional (QTP) Question:

There are four types of parameters:
Test, action or component parameters enable you to use values passed from your test or component, or values from other actions in your test.
Data Table parameters enable you to create a data-driven test (or action) that runs several times using the data you supply. In each repetition, or iteration, QuickTest uses a different value from the Data Table.
Environment variable parameters enable you to use variable values from other sources during the run session. These may be values you supply, or values that QuickTest generates for you based on conditions and options you choose.
Random number parameters enable you to insert random numbers as values in your test or component. For example, to check how your application handles small and large ticket orders, you can have QuickTest generate a random number and insert it in a number of tickets edit field.