The put/call ratio is an important indicator of market sentiment and the possible future direction of the market. It is calculated by dividing total number of put options traded over a particular security and dividing it by the number of calls traded over the same security.
A ratio over one means that more puts than calls have traded during the day, possibly indicating a bearish market for the underlying security and its options. A ratio under one means that calls are more popular than puts, potentially indicating a bullish market.
This ratio is updated live as trades occur during the day. A second ratio, the put/call OI ratio, is also calculated at the end of each trading day, using the open interest for puts and calls over the security. You can view both ratios by searching for an underlying security on the ETO page.