What is the use of SeeAllData = True in test class in salesforce?

Hi Laveena,

use the isTest(SeeAllData=true) annotation to grant test classes and individual test methods access to all data in the organization,
1) If a test class is defined with the isTest(SeeAllData=true) annotation, this annotation applies to all its test methods whether the test methods are defined with the @isTest annotation or the test method keyword
2) The isTest(SeeAllData=true) annotation is used to open up data access when applied at the class or method level