The term gem is often used to define relatively new coins with lower market cap, but showcase a huge potential and are grossly undervalued. It can get tricky at times to actually find gems, that have the potential to boom over time.
Some of the few criteria to scalp gems include rigorous fundamental analysis, understanding its market cap, supply, and volume. Oftentimes, hidden gems have some form of scarcity mechanism to cap the monetary supply.
It can be either based on a deflationary model like Bitcoin or based on an inflationary one. In fact, some of the most commonly traded cryptocurrencies in the world were once a gem. However, try to focus on fundamental analysis and research prior to investing in a potential gem.