Road bike wheels are typically 700c size, although the smaller 650b size can be found on some smaller frames. Regardless of size, both are available as carbon or alloy options.
Carbon fibre rims are used on most of the best road bike wheelsets. These rims lower weight and are often deeper, to improve aerodynamics over a shallow wheel. In fact carbon can be produced in a far greater range of shapes, allowing manufacturers to create wheels optimised for a varied range of riding styles.
Alloy rims are generally cheaper and will feature on many complete road bikes. They are usually heavier than their carbon counterparts although lightweight alloy options are available.
Wheels are a component where bike makers often look to economise, so a budget wheelset may feature even on an expensive bike. It’s worth considering whether you’ll need to upgrade them to get the best out of your new bike.