Glossy sets are cards that feature a shiny, reflective coating — achieved through printing technology like chromium paper (Chrome cards) or other premium finishes. The visual pop of a glossy card is immediately noticeable compared to a standard matte or non-glossy card.
Glossy sets are typically produced in more limited quantities than their regular counterparts, which adds both collectibility and value. Examples include Chrome sets, Tiffany Sets from the '80s and '90s, refractors, and various inserts or subsets packaged inside non-glossy products.
If you're drawn to cards that catch the light and look premium in hand, glossy is the way to go.