plasma5 mean the same thing.
As explained by the Super User equivalent, Plasma 5 is the fifth iteration of KDE's desktop environment (
kde5, on its own, makes no sense).
For this reason I'm in favour of migrating/burninating
kde5 to be replaced with
However, many people don't realise their environment is called "plasma", someone asking a question may begin to type in "kde" as a tag; it won't auto-suggest
plasma5 for them (as
kde5 would be).
I solved this on SU by naming the tag
Almost all questions I looked at under either of these tags were tagged with the other also.
Whether we move both, keep plasma, or keep kde, they do need to be merged.