its alot to explain. basically, its the output that the battery can handle. i came across a couple threads that go into detail.
http://www.e-cigarette-forum.com/forum/ecf-library/129569-rechargeable-batteries.html
and
http://www.e-cigarette-forum.com/forum/battery-issues/475473-how-does-resistance-affect-battery-drain.html
you can browse through these and hopefully learn a few things. if not, use the search button in this forum.
you can also google: "sub-ohm vaping" and "ohms law" and "30 amp battery vs 10 amp battery". its alot of info to take in, i know. but better than your mod/battery blowing up in your face because you were ignorant.
basically, (veterans: correct me if im wrong!) but depending on how you wrap your coils, the resistance (ohms) is a variable, and it puts strain on the battery. for example, if im running a .5 ohm coil on a freshly charged battery with a 4.2v output, (according to
Ohm's Law Calculator i'd be pushing 35 watts at 8.4 amps.
i know theres a thread on this forum about battery safety and what batteries are best for certain configurations. i just cant seem to find it. if i come across it again, i'll post it here. sorry i cant be of more assistance.