The total resistance is a percentage (maxing out at 66), but how the contributions to that are calculated vary. From the

Dragon Knight Saga FAQ/Guide:

MELEE RESISTANCE, RANGED RESISTANCE, MAGIC RESISTANCE

Melee Icon: Red shield with crossed swords.

Ranged Icon: Green shield with a bow.

Magic icon: Blue shield with a white energy ball.

The percentage of damage from attacks of the corresponding type that you resist. A melee resist of 50% means you take half the melee damage you would at 0%. The stat is shown in percentage, but all increases occur in the form of vague, undefined "points," with one point equaling much less than 1% of resistance, and decreasing in value the higher the resistance is.

Resistance from stats is different than from armour. Each point gained from equipped armour is worth a full point, thus an armour that gives +5 to Melee Resistance gives a full 5 points. Each point in a stat is worth 40% of an armour point (or 0.4 of an armour point). Five stat points would have the same effect as 2 armour points (so that +5 Melee Resist armour is 20 Strength worth of defense).