Sugaring refers to either adding sugar to a dish, or covering a specific foodstuff with sugar. Covering a foodstuff (ie fruit) with sugar forms a barrier to microbes, bacteria preventing them from multiplying quickly, hence increasing the shelf life of the foodstuff.
There is a risk in this method as sugar is believed to attract moisture very fast. When the atmospheric moisture is high in content, the yeast present in the environment starts its action and sugar starts fermenting into carbon-di-oxide and alcohol.