What does -> mean in WordPress?

NO -> is not wordpress specific, it is object operator in php.

When you want to call a method of an instance then you call the method with ->

Class SomeClass{

  function example(){
   return 'This is an example function'
  }

}
$obj = new SomeClass();
$obj->example(); // we are calling example function with -> operator

Additional Info: there is one more operator :: which is used to call for static methods of a class.