Cyclocross is a bike racing discipline that involves riding a drop-handlebar bike on a short, off-road course. Courses include features like mud, sandpits, barriers and steps or slopes too steep to ride, forcing riders to run, as well as easier sections. A cyclocross bike is designed specifically for this form of racing, and its design serves its purpose of going fast, and being able to be carried when the terrain demands.
Most gravel/adventure bikes are not purpose-specific racers. Rather they’re designed for long days in the saddle on a mixture of surfaces and terrains and for riding with various types of luggage on multi-day trips.
The key difference between gravel/adventure bikes and old-fashioned touring bikes is the ability to tackle unsurfaced trails, tracks and dirt roads. A gravel/adventure bike combines the multiple hand positions of a road bike with the go-anywhere abilities of a mountain bike.