A compressor is sometimes a limiter, but a limiter is never a compressor. Let me explain. A dynamic range compressor is essentially a tool that takes any given signal and - when used correctly - can lower the volume peaks of a track but can also be used to make the softer parts loud, ultimately giving the entire track a more balanced volume output. Imagine if you have a song that starts off with some low volume vocals, such as a whisper or spoken word, and then sometime after that the song begins to reach its climax, complete with big guitars, loud drums and screaming vocals. Without a compressor, those quiet vocals might be completely muted by the time you adjust the volume of your louder segments. Conversely, if you were to raise the whispers loud enough to be heard, the initial louder parts will be ridiculously loud.
Essentially, a compressor compresses the dynamic (volume) range of the track. A limiter on the other hand limits the amount of a signal passing through. Both use a user dialed in volume output cap (known as the threshold) but instead of taking the the volume overage and compressing it, a limiter just completely removes it. One more time just to get this crucial point across; the main difference between the two is that a compressor squeezes down excess sound while a limiter completely removes it.
Also, compressor can be used as a sort of limiter as long as its ratio setting is sufficiently high. Let elaborate on that a bit. A compressor works through a few settings. You have the threshold which - usually expressed in decibels - acts like the cap. Any volume that goes above this threshold will get compressed. The amount of compression applied to the signal that goes above the threshold is based on the ratio. Pretty much, if you set this ratio pretty high, let’s say anything above 10:1, the compressor essentially becomes a limiter since is squeezes the signal so much that as far as our ears are concerned, the compressed signal is not there. Technically, its still there though, so its not exactly like a limiter - just remember that in case someone tries to pop quiz you. But even when a compressor acts like a limiter, they still sound a little different from each other.
Check out our compressor/limiter section!