There are exceptions to every rule, but the differences between a cyclocross bike and a

mountain bike - Cyclocross bike will have 700c wheels and thinner tires with smoother tread. Usually no suspension, and drop handlebars.

road bike - Cyclocross bike has more frame clearance for fatter tires, and cantilever brakes for better stopping power and mud clearance. Smaller gears for off-road riding.

hybrid - difficult to generalize about hybrids these days, as there are so many different kinds.