Test cases
            It is the step by step description of the 
action that we do during the testing.

Test script
     Type of test file. It is a set of instructions run 
automatically by a software or hardware test tool.

Test suite or secnario
        Is the collection of test cases.
Test plan
      Is a document that describes the objective, scope and 
the approch of the testing. This document has time 
scheduling the teesting activities, and what is assigned to 
whom.

Hi Purni,

Test Script is not a type of file. If a Test case is 
automated , then its a test script. A test script contains 
code. 
In winrunner - its similar to C
In QTP - VB Script
In Silk - 4T
in Rational - VB

Test Suite - Collection of test cases

Test Scenario - End to end flow of a product.

Test Case : A Set of input values, execution precondition,
expected result and execution post condition developed for a
particular object or test condition. 

Test Suite : A Set of several test cases for a component or
a system under test. Where the postcondition of one test is
often used as the precondition for the next one. 

Test Script : A document specifying a sequence of action for
the execution of test. 
(Test Scripts are mostly used in Automation rather than
Manual, anyway the concept is same for both). 

Test Scenario : Test Scenario is mostly likely a Test Script. 

Test Plan : A document descibing the objective, scope and
approach, resourse and schedule of intended test activities. 
Which includes
- Test Items
- Object to be tested and not to be tested. 
- Risk analysis.
- Resource allocation 
- Who will do each task. 
- Entry and Exit criteria

Hi Jason,
               Thanks for correcting me. Later I realized 
it, but didn't get chance to update my answer.