The @Alternative CDI annotation allows you to have multiple matching dependencies for a given injection point. This means you can define beans that provide implementations for the same interface without worrying about ambigious dependency errors. When you mark a class with the @Alternative annotation, it is effectively disabled and cannot be considered for injection. The only exception is for the class that is defined in the beans.xml configuration file.
Once this bean is identified, it is then used in any injection point that matches for this bean. No other beans for similar injection points can be declared as the ‘active’ alternative.
Alternative is really an odd name for it, but all it does is disable the bean while adding it to the beans.xml file enables it and makes it available to CDI.