An alternative plan or method is one that you can use if you do not want to use another one: The opposition parties have so far failed to set out an alternative strategy. An alternative venue for the concert is being sought.

uk / ɒlˈtɜː.nə.tɪv / us / ɑːlˈtɝː.nə.t̬ɪv / An alternative plan or method is one that you can use if you do not want to use...

An alternative plan, method, etc is one that you can use if you do not want to use another one: We can make alternative arrangements if necessary.