This is a technique to execute the function written in machine code or another way where the name of the function is not known, but if it knows where it is.
code is a variable with machine code mounted from that Assembly code in the comments. How to call this through C? Calls can only be through functions. So we have to interpret this array of bytes as if it were a function. C has a way of referencing functions anonymously.
In this case you will have a variable called
ret which is of type "function that returns an integer". The final parentheses in the variable name and pointer (after all function is a pointer to a code) is what indicates that the background is a function.
(int(*)()) is a cast to cause this array to be converted to a function. Not that a conversion is done, it will only be interpreted like this by the compiler. This is done to match what is expected in the variable.
So you can execute arbitrary code. It could come from outside sources, which can be a danger. In some cases the operating system may prevent the execution of arbitrary code.