The term "fret dress" refers to leveling and reshaping the frets. As you play your guitar, the strings wear down the frets because the strings are made out a harder metal than the frets. It is basically like taking a file to a chunk of steel. The steel will get worn down over time from the file. The strings leave little divots in the frets where they come into contact. Dressing the frets levels out these divots and makes the fret perfectly flat again. Then the fret just needs to be re-rounded or crowned. This is a very common repair, as guitar frets will wear down as they are played.
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