What is the difference between synchronous and asynchronous execution?

Answer:

• Synchronous — blocks the current thread until the work is done
• Asynchronous — returns immediately; work continues on another thread or later

// Synchronous — caller waits
let data = try Data(contentsOf: url) // blocks main thread ❌

// Asynchronous — caller continues immediately
Task {
    let data = try await URLSession.shared.data(from: url).0 // non-blocking ✅
}