Cyclocross bikes, what a strange name.
Def: Cyclocross is a cross between road racing and mountain biking. Competitors race laps around a course featuring a variety of surfaces (pavement, grass, sand, gravel, dirt, etc.) while negotiating a number of obstacles that may require them to dismount and remount their bicycle.
Cyclocross Cyclocross bikes are made to travel both on / off road. Cyclocross is actually a competition discipline that developed as something for road racers to do in the off season, however the bikes have grown to be very popular beyond racing because of their versatility.
Combination bikes will typically be heavier than an equivalent road bicycle but lighter when compared to a comparable touring bike. The wheelbase will maintain between that of a street bicycle and a touring bike while the bottom level bracket elevation and headtube angle could be on either part of that of the touring bike with respect to the manufacturer's philosophy.
Tires will be 700c and auto tires will typically range someplace in the 30-40mm width range with small knobs to hold loose surfaces instead of the slicks you will see on dedicated street tires. Framework materials vary widely just like the other bicycle types, but also for top quality cyclocross structures carbon fiber is now a more common material.
Aluminium and metal are also common, especially among middle level bikes and below. Traditional cyclocross gearing is just a little unusual as they typically feature a very close ratio double crankset but this can be compensated for with a wider cassette. Competition dedicated cyclocross bikes may have drillings for drinking water container cages in leading triangle though you'll often see them without containers mounted so they don't really block the way of shouldering the bike over obstacles.
Alternatively, many mix bikes are drilled for racks given that they can dual as a touring bicycle because of the similar geometry. Cross bikes make wonderful commuters due to their flexibility and durability. You could run racks or not, and swap the knobby tires with slicks in the event you so choose.