smogon is one of the biggest pokemon sites, possible tied with serebii.
smogon has got the reputation for its tier listing ability, this puts pokemon into catagories into most use.
UU= under used, this is a pokemon that is not used that often there usually quite weak and not that popular
Bl= border line, pokemon that is quite popular but still quite rare to see on wifi.
OU= Over used, pokemon that have bin abused to much and are the most commong pokemon to see.
there are another 2 groupes
NU= Not used, pokemon that are self explained not used, they are very rare to see on wifi, they are quite the weak pokemon but are quite alright.
Uber= pokemon that are epicly strong, mostly legendary pokemon.
thats basically it..