Sometimes I hear market commentators talk about "buying pressure". But in the market for every trade there is a buyer and a seller. How can there be "buying pressure" or "selling pressure"; aren't those both just high volume?
Buying pressure is when there are more buy orders than sell orders outstanding. Just because someone wants to buy a stock doesn't mean there's a seller ready to fill that order. When there's buying pressure, stock prices rise. When there's selling pressure, stock prices fall.
There can be high volume where buying and selling are roughly equal, in which case share prices wouldn't move much.
The market makers who actually fill buy and sell orders for stock will raise share prices in the face of buying pressure and lower them in the face of selling pressure. That's because they get to keep the margin between what they bought shares from a seller for and what they can sell them to a new buyer for.
Here's an explanation from InvestorPlace.com about "buying pressure":
Buying pressure can basically be defined as increasingly higher demand for a particular stock's shares. This demand for shares exceeds the supply and causes the price to rise. ... The strength or weakness of a stock determines how much buying or selling interest will be required to break support and resistance areas.
I hope this helps!
Buying pressure means there are more interested buyers than there are ready sellers putting upward pressure on prices. That might include institutional buyers who are slowly executing buy orders because they still want the best prices possible without clearing out the market.
Buying pressure doesn't have to be related to volume at all. If everyone who owns shares think they are going to be worth far more than recent market prices, they will not offer them for sale. That means there is more demand to buy than there is a supply of shares to be bought. That condition can exist regardless of trading volume.