Siri always makes an effort to understand what a user is trying to do with an app, and is usually quite good at this. However, sometimes it's really hard for Siri to figure out what's going on or what a user is trying to do. To help Siri figure out what a user might mean, you can provide vocabularies. A vocabulary is a set of strings that map to intents or parameters.
There are two ways for you to teach Siri the vocabulary for your app. One way is through a .plist file. This approach is mostly used for when your app has a global vocabulary that applies to all users. If your app can't supply all custom vocabularies in a static file, you can provide them dynamically. This is particularly useful if, for instance, you want to teach Siri about contacts in a messaging app.