What is the little tag that comes up after a word that you typed before in a document supposed to be for?

[Aaron1]

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[Prince]

I can’t see your screenshot, but I think you mean something like this:

If it is, it’s called “Word Completion”. If the word is what you intend to type, just hit Enter and it will appear in full.

You can tinker with this feature at Tools > AutoCorrect Options… > Word Completion.

Tip: You can use Ctrl-Tab to cycle through other long words you’ve type with the same beginning.