I just learned that Meta Stack Exchange has a tag hidden-features and a tag easter-eggs, and apparently at least one site regular sees sufficient difference between these tags to replace one by the other in an edit. But I don't know what the difference is (and the easter-eggs tag wiki excerpt even says it should be used for questions about hidden features), so I'm asking a meta meta question:
What is the difference in usage guidance between these two tags? When should one be used instead of the other?
Or, as there doesn't seem to be much difference in the meaning of the phrases used as tag names (one could argue that not every hidden feature is an Easter egg, but surely at least every Easter egg is a hidden feature), what about synonymising and merging them to make tagging simpler?