Extraído da documentação mono mod_mono :
Mod_mono is an Apache module that is hosted inside Apache. Depending on your configuration the Apache box could be one or a dozen of separate processes, all of these process will send their ASP.NET requests to the mod-mono-server process. The mod-mono-server process in turn can host multiple independent applications. It does this by using Application Domains to isolate the applications from each other, while using a single Mono virtual machine.