flemflam, in absolutely the most basic terms, what you will find is that there is no standard that motor manufacturers go by to list their motors. The easiest types (for me) are the ones that list the motors by size and kv rating.
For instance, you might see a motor listed as a 35-30-1400. That would break down as follows: 35= motor diameter, 30= motor length, 1400= kv rating, or RPM/volt. That motor would be 35mm diameter, 30mm length, and will try to turn 1400 RPM for every volt supplied to it.
Some manufacturers break their motors down by their equivalent Nitro engine as far as output, so you will see (as in E-flite) a Power 10, Power 25, Power 32, etc. In order to find out their exact output, you need to search the motor specs on their website.
Then, you have the ones that list their motors in terms that seem to have nothing to do with power or size, such as Hacker or Tower Pro.

The main things you need to know, are the dimensions, wattage, kv, amperage rating, and operating range.
Dimensions are obvious, you need to know if it will fit your plane, right?
Wattage needs to be known so you know if the output of the motor is right for your plane. As a general rule of thumb, around 100 watts/lb is usually good enough for trainers, and scale type flight. 150 watts/lb is usually good for scale/sport type flight, 200 watts/lb and up for 3D type flight.
Kv rating is sort of your torque rating. The lower the Kv rating, the larger diameter or higher pitch prop you can run. A high Kv rating will mean higher RPM's, so a smaller diameter or lower pitch prop would be neccessary to avoid overdrawing the motor and ESC.
Amperage rating is important, you can figure the wattage output by knowing amperage draw and supply voltage. Amperage X voltage = watts. You also need to know the amperage draw of your setup to make sure it's within the operating range of your motor/ESC. Ultimately, the prop will determine your draw, but there are other factors involved also, such as kv rating and supplied voltage. A Wattmeter is a MUST!
Operating range is pretty obvious, you don't want to go beyond the motor or ESC's capacities, damage will most certainly occur.

Hope this helps.