I'm a mountain biker and recently purchased a road bike. Road biking is still a new thing to me and it's interesting how different it is from mtb.
Someone suggested to switch to "Shallow" handlebars on my Defy 1 for more comfort.
What exactly are shallow handlebars?
How are the dimension of road bars measured?
This will tell you more than you ever imagined could be told about drop-bar geometry.
Basically, the two key dimensions are bar width (obvious) and the "drop"--the distance from the top part to the bottom part (a low value for which would be a shallow bar). But there are other dimensions worth paying attention to.