Askajedi just did a stat write-up that's a little easier to follow than my jumbled mess, and includes a couple more I'd left out:
The Primary Stats
There are six primary stats that you’ll find on gear and weaponry which affect your characters the most. These stats provide multiple bonuses instead of a single increase, and (depending on spec) may have up to 5 different effects for a single point. To sum it up, each stat has multiple effects, and certain ACs and classes get additional bonus effects.
Strength - Increases Melee Damage + Melee Crit
Jedi Knight/Sith Warrior Bonus – Force Damage + Force Crit
Willpower – Increases Force Damage + Force Crit
Jedi Shadow/Sith Assassin Bonus – Melee Damage + Melee Crit
Jedi Sage/Sith Sorcerer Bonus – Healing Power
Aim - Increases Ranged Damage + Ranged Crit
Vanguard/Powertech Bonus - Tech Damage + Tech Crit
Commando/Mercenary Bonus - Tech Damage + Tech Crit + Healing Power
Cunning - Increases Tech Damage + Tech Crit
Gunslinger/Sniper Bonus – Ranged Damage + Ranged Crit
Scoundrel/Operative Bonus – Ranged Damage + Ranged Crit + Healing Power
Endurance - Increases health
Presence – Increases companion damage, companion health, and companion healing
The Power Stats
When you see those primary stats above increasing damage or healing, they’re not actually directly affecting your abilities. Rather, these stats bump up your character’s power stats, of which there are three. In addition to being modified by primary stats, tech/force/power can be found on gear such as weapons and foci/shields.
Power - Generic stat that increases the damage (and healing!) of all of your abilities, regardless of type.
Tech Power – Increases only damage abilities considered “tech,” such as grenades or flamethrowers.
Force Power – Increases only damage abilities considered “force,” such as Telekinetic Throw or Shock.
Healing Power (Tech and Force) – This is actually split up into Healing Power: Tech and Healing Power: Force, but for all intents and purposes they’re the same. Increases the amount healed by all of your healing abilities.
The Secondary Stats
Accuracy Rating – Increases your chance to hit with all attacks. Keep in mind there are separate caps for different types of attacks. If you go over 100% hit, the additional percentage is converted into defense penetration!
Critical Rating – Increases your chance to score a critical hit with all heals and attacks.
Surge Rating – Increases critical bonus damage with all heals and attacks. The default bonus is 50% extra damage/heals on a crit, which this rating improves.
Alacrity Rating - Decreases activation time for all abilities. This includes both casted abilities and channeled abilities.
The Gear-Defining Stats
Due to the extreme amount of gear customization in TOR, developers want you to be able to take any orange item (orange = fully moddable) and use it all the way to max level if you prefer. In order to achieve this, weapons and armor both have a dynamic stat on them which changes based on the level of the mods you have placed inside the item.
Rating – Increases the damage done on a weapon. You’ll see this listed at the very top of a lightsaber or blaster’s tooltip. The stat itself does absolutely nothing except increase the damage done — think of it as the ‘item level’ stat you’re used to seeing in games like World of Warcraft.
Armor – Armor, which you should be more familiar with, increases Energy and Kinetic resistances (more on that later), is the dynamic stat increased on pieces of equipped gear.
So, for an example, if you take an orange lightsaber with all level 1 mods in it, compared to the same lightsaber with all level 10 mods in it, the Rating stat will be much higher, and thus so will it’s damage. Same goes for Armor on those pieces with Armor on them.
The (Singular) PvP Stat
Expertise – Increases damage/healing done and decreases damage taken in PvP situations.
The Defensive Stats
Resistance – There are 4 types of resistance in the game. Energy and Kinetic Resistance are affected by Armor as well as specific resistance stats, whereas Internal and Elemental resistance are only affected by their stats.
Defense Rating – Increases chance to parry melee attacks and deflect ranged attacks.
Shield Chance – For those who equip a shield in their offhand slot, increases the chance for an attack to be partially absorbed by your shield.
Absorption Rating – Increases the amount of damage reduced when an attack is shielded.
Non-Combat Stats:
Social – This bar will fill as you do quests and Flashpoints in groups. When you win a conversation roll, you earn 2pts/person in party, so 8 points in a full group. You still gain 1pt/person for every conversation choice whether you win the roll or not. When you gain enough points to go up a Social Rank, you will unlock a title and access to Social Gear from vendors throughout the galaxy.
Valor – The valor bar fills as you do PvP. Think of this as a PvP experience bar that will grant you access to better gear as you go up in tiers.
Light Side / Dark Side – This gauge acts as a moral barometer. The more light or dark choices you make, the further on the scale you will move. The bar takes into account your total tally of choices though, so 2,000 LS points and 500 DS points would equal out to you being 1,500 points Light Side. You also gain titles for each tier into LS or DS you go.
Affection – This bar will depend on which companion you’re currently viewing. All companions can gain up to 10,000 pts of Affection rating. The choices you make in dialogue with companions out can have large impacts, while gifts can have impact as well, if the selected companion likes the selected gift. As your companion gains more affection for you, they will become more efficient at crafting and they will begin offering companion quests that reveal elements of their backstory.