User-1840559507 posted
In a nutshell, "A Web farm allows you to expand a Web Site across multiple servers. A Web garden allows you to expand a Web Site across multiple CPUs within a single server."
So if for load-balancing purpose you have hosted the site on multiple servers (may be geographically scattered) it is web farm. But if for a higher processing capabilities, you have multiple processors in a single box, then it is web garden.
Both can be set by modifying web.config