What is mean of fix pack in websphere? how do you apply a fix pack?

WebSphere product update is done in terms of “Fix pack” and “interim fix” .Fix packs are the standard maintenance delivery vehicle for Version
6.1. WebSphere Application Server V6.1 provides fix packs containing cumulative fixes
that are updated regularly, roughly at interval of 12 weeks. This provides a consistent
maintenance approach you can follow as you manage your products. Each fix pack
delivery can consist of multiple fix packs for the following components:
− Application Server
− Application Client
− Web server plug-ins
− IBM HTTP Server
− Java SDK
IBM’s product update terminology has changed from earlier releases of
WebSphere.

Type of update:
---------------
1. Release

Definition:
---------
1.This is the term used by WebSphere Development
and Support for a “major” version of WebSphere.
The first two digits of the product version number
identify the release (e.g., 6.1).


2. Fix pack

Definition:
---------
2. This is the term now used to describe a product
update that in fact includes only defect fixes. (The
previous term for this type of update was cumulative
fix.) The version number’s fourth digit identifies a
fix pack (e.g., 6.1.0.10, 6.1.0.11).

3. Fix and Interiam Fix
Definition:
---------
3. These two terms indicate a temporary or emergency
product update focused on a specific defect. (This
type of update used to be referred to as an
emergency fix or efix.) A fix isn’t identified by
digits in the product version number. You’ll find
fixes listed in the output of the versionInfo utility


Depending on the type of update, the acceptance process starts in development
and moves through different test environments to staging and finally to production.
Acceptance of releases should start with the development team environments because
releases contains major product enhancements and changes. Acceptance of fix packs
tends to start in the test team environments. If a test team discovers some incompatibility
between an application and a fix pack, the development team should get involved. Once
the product update has been run through all the testing stages, the operations team can be
confident that the applications will run properly on the updated version of WebSphere
Application Server.
You should install the product updates referred to as fixes (or interim fixes or
efixes) only if your development or test team has determined that a fix is needed in order
for applications running in a given environment to operate properly. IBM intends fixes as
emergency corrections to defective product behavior. If the applications you’re
developing, testing, or running aren’t experiencing the defect addressed by a fix, don’t
install the fix.