According to this website: http://yarpiz.com/67/ypea104-acor (in the website it is mentioned that it is a project aiming to be a resource of academic and professional scientific source codes and tutorials.):
"Originally, the Ant Algorithms are used to solve discrete and combinatorial optimization problems. Various extensions of Ant Colony Optimization (ACO) are proposed to deal with optimization problems, defined in continuous domains. One of the most useful algorithms of this type, is ACOR, the Ant Colony Optimization for Continuous Domains, proposed by Socha and Dorigo, in 2008 (here)."
What is the difference between continuous domains and discrete combinatorial optimization? I appreciate if you could also mention some examples for each type.