That's the first time I've seen it so it must be new. CDN normally stands for Content Delivery Network. So maybe they are trying to host Live on something like AWS.
Mainly posting here to see/track if a staff member jumps in and explains 
What's live2 (cdn) in live chess settings?
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Hi,,
I noticed a new option (live2 (cdn)) in live chess settings and I don't know what it does, can anyone explain?