Refers to something one must attend to, typically a personal or business obligation. Often used in formal situations to explain absence or unavailability.
noun, noun which may take the genitive case particle 'no'
Indicates that something is needed or has a use. Less common than sense 1; often appears in set phrases like 所用の品 (necessary items).
I will be absent from today's meeting due to a prior engagement.
I'm going to Osaka on business.
I gather the necessary items for the trip.