Modern Classical is the music that emphasizes traditional orchestral instruments, but that has an electronic component, such as tape loops, samples, noticable effects, drum machines, and so on. It is sometimes also used for things like string quartet or brass band covers of electronic music, even though the music itself isn’t electronic.

Better not to be used for academic composers, for whom you should use Musique Concrète, Avantgarde, Contemporary (genre: Classical), etc, as appropriate.