keep on see ppl say Thomson router is lousy... what is the problem btw?

Im not a computer or tech guy but does a bad router mean bad wi-fi signal?
Is router a different word for a modem?
Or is it something different?

from my observation. the router will only gila when i torrent.
my house have more than 5 user. and when i run torrent, the router will get really hot. and it will start gila.
after i put a cooler pad to cool down the router, this problem never happen.

but the wifi signal still sucks. tried to change channel also not improve the signal.
My house is double storey.
even the AP signal (upstairs) which i bridge the thomson router(downstairs) is better when im at ground floor.