Software-Defined Radio (SDR) is a very big deal. This is one of the few areas about which I actually knew a little bit, as we were using some very expensive (complicated, confusing, poorly-interfaced, and worst of all, fragile) SDR equipment in Afghanistan in 2006.
The general idea for the layman (in which category I still and probably always will consider myself) is that because of awesome advances in technology over the last few decades, you no longer need purpose-built hardware to do very specific things in radio, but can build general purpose, flexible radio hardware and specify the parameters for your specific use in software, instead.
To use an analogy, playing video games used to require the purchase of arcade game cabinets. And then game consoles. And now you can play a video game on darned near anything. The hardware (e.g. your PC, your phone, your tablet) is general purpose, and the specific application is all done in software. (This is an apt analogy for another reason I’ll get to in a moment.)