When the number of shares currently Bid is larger than the Ask then the market makers have too little inventory. The reason that they have too little inventory is that there is net buying from the market makers. The stock price would be expected to rise.
When the number of shares currently Ask is larger than the Bid then the market makers have too much inventory. The reason that they have too much inventory is that there is net selling to the market makers. The stock price would be expected to fall.