Q:

Proposal: Merge tags: validation & data-validation

The two tags
https://sqa.stackexchange.com/tags/validation/info (6 questions)
https://sqa.stackexchange.com/tags/data-validation/info (3 questions)
have the same text.
Should they be merged, made synonyms, or differentiated?

A:

Yes, the Tag info has exactly the same description and from the terminology as well it seems they would serve similar purposes. 
I think they can be merged to avoid ambiguity.
Quoting from an accepted answer on meta.stackexchange.com:

All good tag synonyms should eventually be merged (source). This
  retags all questions tagged with a synonym – which is not
  automatically done when a synonym is created. As merging is not
  (easily) reversible, it should be done with caution and only when a
  synonym is established. Only moderators can perform a merge.

Synonymizing and merging tags will also make it easy for users when posting questions. The tag suggestions will not have duplicate suggestions. Unambiguous data really helps narrow down search criteria and results!

