Variances in volts, amps/wire speed, and shielding gas.

You should be referring to Spray Metal Transfer, Short Circuit Transfer, and Globular.  Also Pulsed, but it is generally Spray that pulses at a set frequency to get the desired results.

Short arc is done at low voltage and slower wire speeds with either pure CO2 or Ar/CO2 75/25 mix.
Spray is at higher voltage and faster wire speeds with Ar/CO2 80/20 or higher.  I generally prefer 90/10 or 95/5 and even 98/2.  The 98/2 is Ar/Oxy.
Globular, is globular.  Describes itself well. 

Have a Great Day,  Brent

Globular transfer is what You get if You run CO2 at voltages& wire speeds higher than what gives short circuit transfer. The penetration is great, but the "globs" go EVERYWHERE. When the job is done it looks like coarse steel shot has been fused to a large area all around the weld. This crap sticks well, and needs to be chisled or ground off.

I don't know if globular transfer is used much anymore, We used it for heavy plate weldments at the auto frame manufacturer due to the low cost of CO2. The cost to clean around welds is much greater than the savings on the cheaper gas. Spray transfer gives much cleaner results.

A surprising question for a CWI.

Any welding textbook and several of your CWI study materials can provide pretty good definitions.

Spray and Globular transfers are both "open Arc" modes... This means that the electrode wire does not touch the work (puddle) while it deposits the metal.. 

Spray tranfer has an open arc and the droplets are smaller than the diameter of the electrode wire. Spray transfer requries a shield gas composition of at least 80% argon. The small droplets are actually drawn into the puddle axially with the field of the arc plasma...  This is why it is often called "Axial spray transfer".

Globular transfer can actually be achieved with any GMAW shield gas...  It will occur at a current and voltage combination that allows for an open arc, but the droplet size remains as large or larger than the electrode wire.

An example of spray transfer parameters for mild steel would be something like  0.035 ER70S-X filler  400 inches per minute and 26 volts, with a shield gas of 90% argon and 10% CO2...   If you reduced the voltage to about 24 the arc would remain open, but the droplets would be larger and this could be described as globular.  If you reduced the voltage even more... Say to 19 or less, the electrode wire would touch the work/puddle, melt, open an arc for a short time until the feed pushed the wire back into the puddle to make another short circuit,, this pattern is referred to as "short circuit transfer"

Globular can also occur with short circuiting gasses like  75/25 AR/CO2  or even pure carbon dioxide at voltages and wire feed speeds that are above short circuiting range... An example would be  100% C02  .035 ER70S-X electrode wire  250 inches per minute and 23 volts....  In this type of globular transfer the CO2 gas actually causes a repelling effect on the open arc transfer and the weld droplets fly all about, unlike the drawing axial effect mentioned above, causing considerable spatter.

There are two other transfers seldom discussed (and quite frankly I don't know where they are used). High Current Density Rotational Spray and High Current Density Non Rotational Spray Transfer. It can be argued they are variants of spray but the phenomena is so different I would tend to argue they should be considered transfers of their own.