Waveguides have been mentioned a few times in this blog (i. e. here and here), so it seems quite apt to explain (in laymans words) what a waveguide is. As any serious pundit, I will start by quoting the internets source of everlasting wisdom:
„A waveguide is a structure that guides waves, such as electromagnetic or sound waves.“
This, of course, does not really help, since the reader can guess this definition just from reading the word „waveguide“. But we learn, at least, that a waveguide is not a person but a structure, unlike – for example – a tour guide. Let’s try again to find out what a waveguide is by picking the word apart:
What’s a wave? Luckily, due to discovery of the wave-particle duality in the last century, the answer is quite clear: Almost everything is a wave. So, that’s done.