Skills

Skills are features/abilities a player can use in a game. These can be trained and leveled up to gain perks or abilities for the skill. There are various types of skills in the game including: Sword Skills, General Skills, Unique Skills, Outside System Skills, Original Sword Skills and Extra Skills.

Background
There are several different classes of Weapon Skills. There are generic weapon skills such as «One-handed Straight Sword»and «One-handed Curved Sword». Then, there are additional weapon skills that can be unlocked after fulfilling a certain set of conditions. For example, in the sword category, the «One-handed Straight Sword» skill must be trained quite a bit before «Rapier» and «Two-Handed Sword» appears on the weapon skills list.

Weapon skills that do not have clear conditions for appearing are called Extra Skills. There are roughly around ten known Extra Skills, including the «Katana Skill» wielded by Klein. Each of these extra skills have at least ten people in the Sword Art Online world who practice the skill.

There are only two known Unique Skills, which are weapon skills unique to a single player. These are Heathcliff's «Holy Sword» and Kirito's «Dual Blades».

List of General Skills in Sword Art Online
In general, skills must be equipped in a limited amount of skill slots. Kirito, at the end of SAO, had 12 skill slots. Skills may be trained up to level 1000, at which it is considered «Mastered». There is rumored to be an unlimited number of skills in Sword Art Online.

Non-Combat Skills

 * Fishing
 * Musical Instrument
 * Sewing
 * Cooking
 * Equipment Appraisal
 * Tools Appraisal
 * Purchase Negotiation
 * Sales Negotiation
 * Medicine Mixing
 * Slash Weapon Forging
 * Thrust Weapon Forging
 * Blunt Weapon Forging
 * Light Metal Armor Forging
 * Heavy Metal Armor Forging
 * Metal Equipment Repairing
 * Metal Refining
 * Familiar Recovery
 * Familiar Communication

Passive Skills

 * Searching
 * Tracking
 * Pursuit - Raises effectiveness while hunting monsters. Can be used to pursue a player whose name is known by displaying their footprints from a certain time, which can be increased with greater mastery of the skill. Requires «Tracking» to unlock.
 * Listening
 * Detection - Prevents ambushes. Greater mastery allows detection of monsters in «Hiding» status.
 * Hiding - Allows for a person to disappear. Only works on targets that use visual tracking.
 * Acrobatics
 * Night Vision
 * X-Ray Vision
 * Sprint
 * Extended Weight Limit

Combat Skills

 * Parry
 * Delay - Interrupts opponents attacks whenever possible.
 * Howl - Attracts the attention of NPC monsters and increases a player's Hate status effect. Often used by Tanks.
 * Battle Healing - Recover certain amount of HP over time during battle. It can be leveled up by constantly getting one's HP into the red zone.
 * Emergency Recovery
 * Meditation - «Extra Skill» Increases HP regeneration and decreases the remaining time of negative statuses by entering a mental concentration pose. Obtained in a 6th floor quest.
 * Light Metal Equipment
 * Light Shield Equipment
 * Leather Equipment
 * Heavy Metal Equipment
 * Spirit Light (hate skill)
 * Fighting Spirit (hate skill)

Weapon Skills

 * One Handed Straight Sword
 * One Handed Curved Blade
 * One Handed Dagger
 * One Handed Rapier
 * One Handed Assault Spear
 * One Handed War Hammer
 * Two Handed Straight Sword
 * Two Handed Assault Spear
 * Two-Handed Battle Axe
 * Blade Throwing
 * Martial Arts - «Extra Skill» Unlocked from a quest on the 2nd floor.
 * Katana - «Extra Skill» Unlocked by frequent usage of One-handed Curved Blade.
 * Dual Blades - «Unique Skill» Given to the player with the fastest reaction time.
 * ​Holy Sword - «Unique Skill»
 * Darkness Blade - «Unique Skill»
 * Battoujutsu - «Unique Skill» Means "Sword Drawing."
 * Shurikenjutsu - «Unique Skill» Means "Concealed Weapons."
 * Infinite Spear - «Unique Skill»