Is it possible to define a property in a protocol interface?

Yes, in Swift, properties can be defined in protocols. You can specify whether they are read-only (get) or read-write (get set).

Example:

protocol SomeProtocol {
    var name: String { get set }  // read-write property
    var id: Int { get }           // read-only property
}

Classes, structures, or enumerations that conform to this protocol must provide implementations for these properties.