The term 'side of a gem' can be summarized by the crossword solution 'FACET, ' which is a five-letter word. A FACET is a flat surface on a cut gemstone, usually with a specific angle and shape. Facets are used to reflect light and create a sparkle in the gemstone. Faceting is an ancient art form that has been practiced for centuries, and it is still used today to create beautiful and unique gemstones.