Virtual Hosting: Just think about a home in which inhabitants use the common resources like electricity, gas, water, and many other gadgets. In the same way a web server works in which several websites utilize the common resources to meet their requirements. Virtual web hosting works on the same pattern and especially designed for the middle size organizations into the business with limited budget. However, they are being provided limited control panel functionality. In other words it's a form of cheap web hosting or free webhosting plan.
Dedicated Servers: On the other hand if you go for a dedicated server also named as physical hosting, hands you over a particular web server on which only one site is hosted. Usually, this is used for large scale projects that require uninterpretable bandwidth and web space. Only the issue with dedicated server is the cost; software and hardware both are very expansive and difficult to maintain. This server is most of the times handled by web hosting providing company, that's why called co-location server.
Virtual Dedicated Servers: It lies in between virtual and dedicated servers. There is a single server for several sites but the amount of bandwidth and web space is fixed for everyone depending on the needs of the websites.
MySQL and PHP hosting: There is a great variation in hosting depending on these two technologies. However, PHP hosting is getting more popular among the webmasters. The reason behind is that PHP hosting support is easily available. But if you are looking for some forums at your website, MySQL hosting would be more effective.