See it very simple.Paramerisation is what suppose if we 
want chek something for morethan one value then definatly 
putting that value as constant doesnt help at all.So there 
is only one mean we make them as Parameter and this process 
is called parameterization.
4 ways of doing this
1> Data table
2>Random Number
3>Environment 
4>Test/Action/Component

If u want to check how ur application behaves for different 
input data we can go for parameterization.
 U can parameterize the input data u give.
 Paramerization is of 4 types
1. Test,action or component parameters
2.data table parameters
3.Environment variable parameters
4.Random number parameters

a generic answer (not related to just WR/QTP):
parameterization is a process to get the correct output 
results for different input values that are passed into a 
single variable.
method: 
-define a variable in the script
-create or re-direct the user to generate a data table that 
holds the respective values
-run the script

perameterization is a process of replacing single value 
with multiple variable 
tools --> datadriver--->in datadriverwindow click paramerize
-->peramerize all--->click ok