Optionals in Swift are used to represent absence of value. When a value is of optional type, it either has a value or no value at all(nil). When a value is declared to be optional, automatically its value will be assigned as nil. Except for optional type no other type can be assigned with nil value.
var myOptionalString: String = "Albatross"
var myOptionalNumber: Double! = 12.5
var myOptionalInteger: String? = nil