anoopjose,
A mod N counter is a counter that has N states. Its output frequency is f/N.
For example, a simple 4 bit binary counter is a mod 16 counter.
Regards,
Kral
A mod n counter can also be termed as divide by n counter that divides the clock frequency by n. The divided frequency output is obtained from the MSB of the counter. The counter may be synchronous or asynchronous. In synchronous counter design, the clock is given simutaneously to all Flip Flops whereas in asynchronous design, the clock is given as an input to tha LSB flip flop.