Skills are specific set of keyword abilities (bolded text referring to larger effects).
Skills are differentiated from other keywords in that they can appear on a unit with no other text. For example, a unit can have the Flying or Warp skills as stand-alone keywords, but cannot have Infiltrate or Stun without some additional context. Note that some skills can appear as stand-alone on spells (e.g. Lifesteal, Echo) while other cannot (e.g. Ambush, Berserk).
Like all keywords, hovering over cards with skills will display a box explaining what they do.
Battle skills are skills that would have an effect if a Unit that has it is in play:
Protected from one enemy spell or effect (but not from battle damage).
When this attacks, you may give it Reckless to attack a second time this turn. Can only be used once.
Can attack the turn it is played.
Kills any unit it damages.
|Double Damage: |
Deals double damage.
Readies at the start and end of your turn, and can't be stunned or exhausted by enemy spells or effects.
Can only be blocked by other units with flying.
May be exhausted one time to attack any enemy unit.
When this deals damage, you gain that much .
When this hits an enemy unit, leftover damage is dealt to the enemy player or site.
When this kills a blocking unit, the blocker doesn't deal damage back.
This must attack.
The first time this is killed, give it Destiny and put it into the top ten cards or your deck.
Cannot be blocked.
When this attacks, the top unit or weapon of your deck gets +1/+1.
These other skills are not battle skills, as their effects are relevant while not in play:
Can be played to block an enemy attack or at the end of their turn.
When played, you may exhaust another unit of the same type to reduce this card’s cost by the exhausted unit’s .
Automatically play when drawn, then draw another card.
Get an additional copy when drawn.
On your first turn, a card with Pledge can be played as a Sigil.
This card can't leave the void.
You can play this from the top of your deck.
Skills are defined in the Eternal Rulebook  as "bolded terms with no additional text." However, there are some cards which use different sets of skills for their effects.
As of Defiance, there are only two cards that reference "skills" as opposed to "battle skills" - Divining Rod and Crown of Possibilities. Divining Rod refers to all of the skills listed on this page, while Crown of Possibilities will never give Pledge, Voidbound, or Warp.