Hi Dale,
Z at the end usually means that its a bundle part number. this 5508 might be bundled with few APs and Licenses to get started
have a look at the attached from my past purchases,that included 2 APs and 25 licenses,For your part number have a look at the ordering guide
Also you may already know that Z(AIR-X-Z-K9) could be also in the APs which is the one of the regions,different to this one
Cheers
Prabath
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-Prabath