Dexterity

Dexterity (Dex) encompasses several physical attributes including hand-eye coordination, agility, reaction speed, reflexes, and balance. Dexterity affects a character's reaction to a threat or surprise, their accuracy with thrown weapons and bows, and their ability to dodge an enemy's blows. It is the prime requisite of rogues and affects their professional skills. A rogue with a Dexterity score of 16 or higher gains a 10% bonus to the experience points they earn.

Explanations
Reaction Adjustment modifies the die roll to see if a character is surprised when they unexpectedly encounter NPCs. The more positive the modifier, the less likely the character is to be surprised.

Missile Attack Adjustment is used to modify a character's die roll whenever they use a missile weapon (a bow or a thrown weapon). A positive number makes it easier for the character to hit with a missile, while a negative number makes it harder.

Defensive Adjustment applies to a character's saving throws against attacks that can be dodged - lightning bolts, boulders, etc. It also modifies the character's Armor Class, representing their ability to dodge normal missiles and parry weapon thrusts. (In some situations, beneficial Dexterity modifiers to Armor Class do not apply. Usually this occurs when a character is attacked from behind or when their movement is restricted - attacked while prone, tied up, on a ledge, climbing a rope, etc.)