Hi,

there are different terms associated with test plans (schedule, key
date) that later, when executing a test suite I think these terms have
been translated to test milestone.

There is also a category that can be associated to test plan called
release.

And I can also create snapshots but these are not associated with any of
the above terms?.

Which is the exact relationship between all above terms? Do you have a
clear scenario description of how I should use them in a real scenario?

I see many terms, but don't have a clear idea of the objective of each one.

Many thanks in advance

the Schedule is indeed the listing of what will be translated to be Milestones when you're executing test - could also be referred to as "iterations". the Key Dates are used to identify items like "code freeze" etc

The category of "release" is actually user configurable - its not mandatory and can be removed or renamed to something more appropriate that you want to see against your test plans.

For me, I use the scheduled dates, as my "test cycles" - which are selectable as the milestones. The Key dates I do use exactly for the purpose above to ensure that we have visibility to any system outages.

The release I actually took out of the categories entirely.

Looks like nerack has covered the specifics of what you are asking. For more general terminology definitions, you might want to take a look at the ISQTB work being done on a glossary for testing and related terms; this set of terminology was followed when RQM was created -
http://www.istqb.org/Working_Party_ISTQB_Glossary.htm

There is a link to their latest Glossary document at the bottom of the page.