Grading is the process of submitting your cards to a third-party service that evaluates their physical condition and assigns a numerical grade from 1 to 10. The higher the number, the better the condition — and the more the card is typically worth.
A perfect card earns a GEM Mint 10, which is the holy grail of grading. Mint and near-mint grades command exponentially higher prices than lower-graded copies of the same card. We're talking multiples, not just a little bump.
The grading process also encases your card in a tamper-proof slab, which protects it and confirms its grade for future buyers. If you've got a card you think is special, getting it graded can unlock serious value.