You heard right. They are both electromagnetic waves. The difference is their frequency.
Radio waves range from 3 KHz - 300 GHz where as visible light ranges from 430-770 THz.
Yes, all electromagnetic waves travel at the speed of light in vacuum. Traveling through materials things get a bit more complicated.
The term "invisible light" seems to me a contradiction- "light" pretty much means "visible electromagnetic radiation".
Romsek, correctly, referred to the difference between "light" and "radio waves" as one of frequency. I tend to think of it as a "wave length" (of course, a specific frequency gives a specific wave length). Light has wave length on the order of \(\displaystyle 10^{-7}\) m while radio waves length is on the order of several hundred meters, a "city block" or more.
Romsek, correctly, referred to the difference between "light" and "radio waves" as one of frequency. I tend to think of it as a "wave length" (of course, a specific frequency gives a specific wave length). Light has wave length on the order of \(\displaystyle 10^{-7}\) m while radio waves length is on the order of several hundred meters, a "city block" or more.
The term "Light" is very human-centric.
It is just the (tiny) part of the electromagnetic to which our eyes are sensitive.
There are animals that can see (a small way) into the ultraviolet (above violet in the rainbow) and infrared (below red).
Microwaves and Radio Waves are infra-infrared
X-Rays and Gamma Rays are ultra-ultraviolet
The names we give these regions of the electromagnetic spectrum are principally historical,
and where one becomes the other is simply a fairly arbitrary (and not particularly clearly defined) convention,
dreamt up by the people who deal with these portions of the electromagnetic spectrum.
It is just the (tiny) part of the electromagnetic to which our eyes are sensitive.
There are animals that can see (a small way) into the ultraviolet (above violet in the rainbow) and infrared (below red).
Microwaves and Radio Waves are infra-infrared
X-Rays and Gamma Rays are ultra-ultraviolet
The names we give these regions of the electromagnetic spectrum are principally historical,
and where one becomes the other is simply a fairly arbitrary (and not particularly clearly defined) convention,
dreamt up by the people who deal with these portions of the electromagnetic spectrum.
On the other hand (this occurred to me while I was writing my previous answer but I decided not to mention it), we do refer to "ultra-violet light" and "infra-red light". So many scientists use "light" to refer to a somewhat larger region of the spectrum than just "visible light". But still only a relatively small portion.