drewfx1
If it were up to me I would say a "brick wall" limiter implies an infinity to one ratio.

I mostly agree.. I always thought that higher ratios  (above 15:1) was making the compressor "limit" the signal.  Thus if the ratio is sufficiently high enough in that very little "discernable" signal came through... then this was the brickwall effect. Where I  slightly diverge is that this could happen.. depending on the signal before the infinite:1 setting is reached. 
Kinda I guess like Cognac... All Cognac is Brandy .. But not all Brandy can be classified as Cognac.. All limiters are  considered high compressor settings,  but not all compressor settings can be considered limiting. I guess....

But isn't what you describe actually a compressor

No!!! A compressor has a ratio of less than 10:1.  My example said the ratio was 12:1. This is greater than 10:1, so that would be limiting, not compression
 
Compression stops when the ratio is higher than 10:1 and limiting starts.
 

You could consider a limiter as a compressor with fewer options; or view a compressor as a limiter with more variable controls. Generally a compressor constricts the dynamic range and therefore allows a higher overall volume; while a limiter is more often used mainly to catch transient peaks. Of course, both are used creatively for many things.

And then you have a Maximizer. which brickwall limits cleanly and then you got a Clipper that softens the peaks LOL
 
You have a compressor and above 10 or 20:1 you have a limiter.
Brickwall limiter could be called a Maximizer and a Clipper a Leveling Amp.
 
Different designs overlap. 
 
 

I use the Waves L2 for "finalizing" levels on the mixes.  It's reasonably transparent too.  You can pick it up for $99 sometimes.  Does the gig for sure.

CJaysMusic

But isn't what you describe actually a compressor

No!!! A compressor has a ratio of less than 10:1.  

Please post the source of your statement. 
 
 
 
Compressor
When the input reaches the threshold level the output gain is reduced by an amount set by the reduction ratio control. Some units have fixed choices 2:1  4:1  10:1  20:1 etc.  others are continuously variable from 1:1 (no effect) to infinity:1 (limiting*)
The speed with which the output gain changes is generally "slow" by comparison to the waveform being processed, more closely following a time shifted average of the waveform amplitude. (RMS)
The slow attack will let through the initial transient peak of percussive sounds before the gain reduction takes effect, then the slow release reduces the overall volume of any following waveform. The slow change in output gain is akin to "riding the level" with a fader and as such there should be no perceptable distortion to the signal.
The "normal" mode of operation would be to have the threshold level set such that the compressor is actively controlling the signal most of the time.
*see exceptions
 
Limiter
A limiter controls the output with a variable gain stage just like a compressor, however the attack and release times are so fast it follows the specific value of the input waveform, not it's average value.
Once the value of the waveform exceeds the threshold level the limiter applies all gain reduction necessary to prevent (limit) the output from going any higher.   In the digital domain that we now work in where all signals are processed by pure math, this would result in perfectly flat tops with sharp edges to all the waveform that reaches the threshold level.  This is what a limiter does.
In reality it sounds absolutely horrid!!  so the attack/release times are slowed down just a fraction (micro seconds) to round off the edges and smooth out the gain changes enough to reduce the resulting distortion to a more musical, hopefully inaudible, level.  The way the gain reduction is smoothed is the main difference between different brands/models of limiters.
Most importantly, because the limiter ONLY affects the peaks of the waveform, it does not affect the overall volume.  As the input volume is increased the perceived output volume will continue to increase, at the cost of higher perceived distortion.
The "normal" mode of operation would be to have the threshold level set such that the limiter is NOT controlling the signal most of the time.
 
 
 
There are obvious exceptions to the "standard" way to use compressors/limiters, which is where most of the arguments start as to what is actually being used to do what...
eg. A compressor set to infinity:1 is working like a limiter, but it is not limiting. Transients will still get through and produce pops and clicks if they cause digital overs...
eg. A limiter will specifically clip transients, but pushed hard enough will affect the rest of the waveform apparently like a compressor, but it's not compressing the entire waveform, it's clipping the tops off...
 
 
YMMV  YCMV  YLW
 
 
(your mileage may vary, your compressor may vary,  your limiter won't)

A true "brickwall" limiter would have (aside from infinity:1 ratio) digital lookahead in order to achive zero attack time!
The general distinction between compressor/limiter isn't fixed but relates more to where the threshold is set. A limiter is set to only act on transients while a compressor is set to affect a larger portion of the dynamic range. Most dynamics plugins/hardware will be able to do both (but not "brickwall" limiting because of the lookahead requirement).

For examples of brick wall limiting simply send off your track to a few cowboys who claim to be great at mastering and look at the final waveforms in something like audacity where the peaks are so truncated it's a total disaster. Then watch the band all agree about how much better it sounds and how they beat the loudness war (no bitterness here hoho!) :)

It is this simple:
A ratio of less than 10:1 = compression
A Ratio of 10:1 or Greater = Limiting
 
This is the difference between compression and limiting.

CJaysMusic
It is this simple:
A ratio of less than 10:1 = compression
A Ratio of 10:1 or Greater = Limiting
 
This is the difference between compression and limiting.

I'm sorry CJ old friend, but that is a silly and imprecise definition IMO! 
 
For example, I could easily compress a very dynamic or sloppily played bass guitar track with a ratio of 10 or 12 to one in order to squeeze it into submission (low dynamic range). With plenty of non-transient action going on above the "knee", I would never call that approach "limiting". 
 
If I wanted to "limit" that same track, I'd set the threshold so that only transients would be caught. The result would be a politer sounding track but it wouldn't kill (or rectify) the dynamic range to the same extent, since only the transients would go above the "knee".
 
The difference is in the application, not in the numbers!