Type alias is technique to provide new name to existing data type without modifying it's original behaviour. That is similar to typedef in C programming language. That are used when simplicity in coding style and that are reliable to provide independence. For example.
typealias shortInt=Int8 var age:shortInt = 20 print(age)
typealias keyword are used to provide a new type alias in Swift programing language. In above example shortInt is a signed 8 bit integer. Once define a aliasing name, and use anywhere within the code.