Component
Some Abilities will list Components needed by the Ability. Components can be generic, like “hands” or “standing,” or a specific, like points from a Point Bank on your Character Sheet. The most common components are #Motions and #Chants, which Spells often need.
If you cannot fulfil a Component when it comes time to roll the Ability's Skill Test, you will receive a Disadvantage for each missing Component. All Components get evaluated when you perform the Test for an Ability, including for Slow Actions, so you do not need to be able to fulfil the Component when starting an Ability.
While you have stacks of Concentrating, if a Component of one of your active Concentration Abilities gets interrupted, you will need to make a Focus Save as described by that Condition.