All dice in 7th Sea are d10's. Under normal circumstances, these dice 'explode'--if you roll a 10, you re-roll that die and add the result to the original. If you roll a 10 again, you add 10 and reroll, until you stop rolling 10's. The total is considered the total value for that one die.
When you roll dice, you typically roll a bunch, then keep the higest. You might roll 5 dice and keep the highest 3. The nomenclature for this is '5k3'.