Short channel is the one in which the drain to substrate depletion increases bcoz of more reverse bias so wt happens is ur channel length becomes shorter..
which is given by Ids=beta(Vgs-Vt)62/2( 1+lamdaVds)
where lamda is the channel length modulation
Added after 5 hours 29 minutes:
Short channel effects
Gate induced drain leakage
Drain induced barrier lowering
Hot electron effect
When the difference between gate to source voltage(Vgs) and the threshold voltage(Vt), is lesser than the drain to source voltage(Vds),(Vds > (Vgs - Vt))then the conducting channel length starts reducing and henceforth various disadvantages related to teh performance of the mosfet as our friends indicated above..
to get better understanding abt short channel we need to know long channel also the book by taur and ning covers the long channel and short channel its good book covering latest concerns in short channel also plz through it