Interface Type Definition

When a field can return one of a heterogeneous set of types, a Interface type is used to describe what types are possible, what fields are in common across all types, as well as a function to determine which type is actually used when the field is resolved.

Example:

const EntityType = new GraphQLInterfaceType({
  name: 'Entity',
  fields: {
    name: { type: GraphQLString }
  }
});