Bid Price - highest price that buyers are willing to pay for
Ask Price - lowest price that sellers are willing to sell at
Bid volume refers to transactions that happen at the bid price
Ask volume refers to transactions that happen at the ask price
Generally, bid price will always be lower than ask price since a transaction occurs when bid = ask.
Hence when bid volume is higher than ask volume, there are more transactions occurring at the bid price, which means that the price is likely to move downwards (cheaper).
Vice versa for ask volume - when ask volume is higher than bid volume, there are more transactions occurring at the ask price, which means that the price is likely to move upwards (more expensive).