the updated opinions I heard on the Random Theory is, that stock markets are mostly random, but with a drift (there is some trending in the market). Just the fact the market pretty much averaged 7-10% for man decades was evidence of this - some due to inflation, etc. But is Trend = Momentum? Depends on how long a time frame being discussed.
I believe that is what people mean when they talk about trends. This stock has been going up and is in an "upward trend" therefore it is more likely than not to continue on moving upward and vice versa.