What does 'digital spectrum' mean?

Question

I googled the term to no avail. What does it mean? I guess it has to do with IT technology, but I am not sure.

Many of the leaders I know in the upper echelons of media industry are intelligent, capable, and upstanding people. But they are leaders of companies that appear to have only one purpose: the single-minded pursuit of short-term profit and "shareholder value." I believe, however, that the media industry, by its very nature and role in our society and global culture, must act differently than other industries especially because they have the free use of our public airwaves and our digital spectrum, and have unfettered access to our children's hearts and minds. These are priceless assets, and the right to use them should necessarily carry serious and long-lasting obligations to further the public good.

The Other Parent: The Inside Story of the Media's Effect on Our Children

Answer 1

The word spectrum originally was used for the visible spectrum of light with its well known range of the colours of the rainbow. Later it has been expanded into other areas and used to apply to anything which lies on a continuum. So we speak of the electromagnetic spectrum (which includes visible light as a subset) but we also speak of the political spectrum where we imagine views on a continuum from left to right.

In the quote the writer is referring to a whole range of digital communication channels like social media, instant messaging and so on.