I was surprised to see String... in Day 11's test:

struct School {
    var staffNames: [String]
    private var studentNames: [String]
    init(staff: String...) {
        self.staffNames = staff
        self.studentNames = [String]()
    }
}
let royalHigh = School(staff: "Mrs Hughes")

So I did some searching and eventually found that it is a Variadic parameter. The Swift language documentation says Int... can be treated like [Int] so I assume String... can be thought of as [String]

Kind of but you can enter the elements with just a ,

let royalHigh = School(staff: "Mrs Hughes", "Mr White", "Miss Scarlet", "Prof Green")

Check this How to make a variadic function Also new in Swift 5.4 Multiple variadic parameters in functions

Thanks @NigelGee