On the Internet, I found the phrase
Function changes a short abbreviation into a text block
For instance, an abbreviation of "US" changes to "United States".
I feel there should be a single verb to express this act. But I can't find it.
In some other languages, e.g. in Russian, Ukrainian, there is such a word with the meaning of "open", "unveil", "open out", "open up", "release". Like a flower or locked box opening. What is it in English? Or would any of the mentioned words work?