A skill is an ability that allows a character to perform some action or make some item that improves with use. The improvement depends on the difficulty of the action or the difficulty in creating the item. Professions are a subset of skills. Not all skills are professions.
There are a few skills that don't improve with use.
- Lockpicking – Required Thieves' Tools before patch 3.0, but no longer needs an item.
- Pickpocketing – Does not improve with use.
Poisons– Prior to patch 3.0, it worked like a profession. It has been removed from the game as a skill, and poisons are instead purchased ready to use.
The death knight only skill is:
- Runeforging – Allows death knights to engrave runes into their weapons, offering a variety of free weapon enchantments. Requires a runeforge.
Combat skills have a maximum skill level of 5 * your current level.
- Defense skill – Improves your ability to avoid attacks. Some gear adds defense rating, which raises your defense skill above its normal maximum.
- Weapon skills (Melee and Ranged) – Each weapon type has an associated skill.
Currently there is no way to learn a new language, except the Murloc quest chain in Borean Tundra (although this skill won't appear in the skills interface).
- Alliance (Common, Darnassian, Dwarven, Gnomish, and Draenei)
- Horde (Orcish, Troll, Taurahe, Thalassian and Gutterspeak)
- Neutral (Goblin, etc.), not available to Player characters.