IBM products have the following structure for version number:

version.release.modification.fixpack

Or, sometimes this is abbreviated, like this.

v.r.m.f

For example, with 9.1.0.2:

• 9 is the version
• 1 is the release
• 0 is the modification
• 2 is the fixpack

Version

When a new version of a product is released, the version number wil increment, like this.

• 7.0.0.0
• 8.0.0.0
• 9.0.0.0
• et cetera

Long Term Release (LTS)

A long term release (LTS) will increment release number, like this. LTS include minor changes and some of the prior CD modifications and interim fixes. New LTS are released less frequently than CD, typically once every two years.

• 9.0.0.0
• 9.1.0.0
• 9.2.0.0
• et cetera

Continous Delivery (CD)

A continous delivery (CD) will increment modification number, like this. The first CD modification will have a value of "1", which means that 9.0.0 does not include a CD modification. CD are released more frequently than LTS, and include enhancements, defect fixes, and security updates, typically once every two months, thus CD is an ideal model if your goal is to frequently obtain the latest fixes.

• 9.0.1.0
• 9.0.2.0
• 9.0.3.0
• et cetera

Fix Pack

A fix will increment the fix pack number, like this. A fix pack is a fix for some type of defect. Fix Packs are downloaded from Fix Central or as a program temporary fix (PTF). Fix packs are cumulative, meaning that newer fix packs contain the fixes from prior fix packs. Fix packs are used with the LTS model, not for the CD model. 

• 9.0.0.1
• 9.0.0.2
• 9.0.0.3
• et cetera

Interim fix / iFix

Since CD a release about once every two months, fixes are not typically applied to a CD release. Instead, the idea is to include the fix in the next CD release. However, for an urgent issue, an interim fix (also known as an iFix) may be made available to fix the issue. interim fixes are used with the CD model, not for the LTS model, and only against the last two CD releases. For example, if the current CD release is 9.0.3, then an interim fix is only available for 9.0.3 and 9.0.2.