Abilities are skills in Wandering Ronin that are granted to ceratin classes based upon their use in the game. Each ability has its own rules and regulations that must be followed, and only certain classes may use certain abilities.
From the Rulebook:
Some classes have specific abilities that are not listed in their description. These are listed below, are always available when your class allows for it, have few restrictions, and are non-negotiable. No activities stop during the use of these abilities, and you are not considered out-of-game while using them (i.e.: you may be killed by another person while looting someone else).