How / where can I learn the meaning of the numbers and letters associated with each camera model?

Question

Also meaning of camera model names such as PowerShot, EOS, etc.
Thanks!

Answer 1

The Powershot series are all point & shoot cameras.  The letter prefer in the model number is a class within the point & shoot category.  The "G" series Powershots, for example, are advanced point & shoot bodies and somewhat high end considering they are point & shoot cameras (they're often the second camera that a DSLR owner will use they're going somewhere that a DSLR is either not permitted or simply not practical.   I had to travel for a busines trip recently and I had room in my bag to throw my G1 X in... but not room for my larger DSLRs and large lenses.
The EOS bodies are all SLR or DSLR (SLR = single lens reflex camera and without that letter "D" on the front it implies it's a "film" camera.  With the letter D it's a "digital" camera.  Canon does not make a "film" SLR anymore -- so that's really a historical note to mention the "SLR" category.)
Within the EOS system, you could break the system into roughly three major groupings... entry, mid-level, and pro.
All "Rebel" series bodies are entry level.  Note that "entry" level for a DSLR is still a world ahead of point & shoots -- so don't think of these as low-end cameras.  In terms of model numbers, in North America, Canon uses a letter/number/suffix combination.  Currently all Rebel bodies start with "T".  The first was the T1i, then T2i, T3i (and T3 without the "i" suffix), T4i, T5i, (and T5 without the "i" suffix), T6i, and T6s.   Higher numbers are more recent models (the T6i and T6s were just introduced a few weeks ago.)  If there is no suffix then it's a more basic model.  The "i" denotes the higher end of the entry range.  But recently Canon introduced the T6s which is the highest end Rebel model and has some features previously only found in mid-level models.
The Rebels include "scene" based shoting modes commonly found on point & shoots in addition to the more advanced shooting modes which are (by far) the most popular among DSLR shooters.  Part of the whole point of buying a DSLR is the incredible boost in image quality you get when you get a camera out of automatic mode, take control of the exposure settings, and use a larger lens and sensor.
The Canon mid-level EOS cameras all have 2 numbers followed by the "D" suffix.  E.g. 10D, 20D, 30D, 40D, 50D, 60D, and 70D (currently only the 60D & 70D are still produced.)  These bodies introduce features found on the pro-level bodies (like the 2nd LCD display on top, extra direct-setting buttons so you don't have to navigate menus, and a 2nd large control dial on the rear) but still retain the entry level features like the "scene" based sooting modes that beginners might use.
The high-level bodies have just one number digit, like 1D, 5D, 6D, and 7D.   But when Canon needs to create a newer version they can't really increase that numberic digit... so instead they rev the model by calling it a "Mark II", "Mark III", "Mark IV". etc.  So it's not really the "5D" these days... it's the 5D Mark III (or simply 5D III).  The 1D is now the 1D X.  The 7D is now the 7D II.
A few odd things happen in this category... first, all of these bodies with the exception of the 7D II get "full frame" sensors.  This is a rather large image sensor which is the same size as a single frame of 35mm film.  It measures roughly 36m wide by 24mm tall.   The entry and mid-level cameras all have "APS-C" size sensors which measures approximately 22mm wide by about 15mm tall (which is very large compared to what a point & shoot camera would have, but not as big as these full-frame sensors.)  When you look at images that have a tack-sharp subject... and yet a beautifully soft out-of-focus background... that requries a large sensor to produce that result.  You can not get that result with a point & shoot or camera phone.
The 7D II still has an APS-C sensor, but it's the best APS-C sensor can makes today.  That camera body is heavily optimized for fast-action photography (the 1D X is also optimized for very fast action shooting and outperforms the 7D II -- but the 1D X is Canon's "flagship" camera -- so no surprise there.)  
The 6D also stands out as that was introduced to be an "entry level" "full-frame" body.  Prior to the 6D, all entry level cameras were basically about $2500 or more (for the body only).  This is a full-frame camera for about $1800 (body only price -- that does not include a lens.)
Incidentally... these pro level bodies finally drop the "scene" based shooting modes that beginner's might use.  They almost might have particularly advanced focusing systems that might even be a bit intimidating for beginners (except for the 6D as that's a bit of an exception.  It's actually considered an "entry level" full-frame camera.  
With the exception of the 6D, I would shy away from recommending Canon's high-end bodies for beginners.  I've found the focus system alone can be intimidating for people and you really do have to dedicate some time to learning the system.  If you don't take the time to learn the system, then you're really wasting your money because these cameras are amazing IF (and only if) you take the time to learn what they can do that other cameras cannot do... and learn when, why, and how to exploit those advantages.  It wont just happpen without some effort on the part of the photographer.)
Tim Campbell
5D II, 5D III, 60Da