Explain the meaning of Ring Counters?

A ring counter is fundamentally a circulating shift register in which the output of the most significant stage is fed back to the input of the least significant stage.

The following is the 4-bit ring counter constructed from D flip-flops and the output of each stage is shifted into the next stage on the positive edge of a clock pulse and if the CLEAR signal is high all the flip-flops except the first one FF0 are reset to 0. FF0 is preset to 1 in its place.

Ever since the count sequence has 4 distinct states the counter can be considered as a mod-4 counter. The Only 4 of the maximum 16 states is used in making ring counters very inefficient in terms of state usage. Except the major advantage of a ring counter over a binary counter is that it is self-decoding. No extra decoding circuit is required to determine what state the counter is in.