No, that's not a typo. That's the reality of virtualization terminology today: a single term means multiple technology implementations.

Server virtualization is used to describe at least two (and probably more) types of virtualization.

1. Server virtualization a la load balancing and application delivery

2. Server virtualization a la VMWare and Microsoft

Server virtualization as implemented by load balancers/application delivery controllers is a M:1 virtualization scheme. An application delivery controller like BIG-IP can make many servers look like one server, a virtual server. This type of server virtualization is used to architect better performing application infrastructures, to provide load balancing, high-availability and failover capabilities, to seamlessly horizontally scale applications, and to centralize security and acceleration functions.

Server virtualization as implemented by virtualization folks like VMWare and Microsoft is actually more properly called operating system virtualization, because it's really virtualizing at the operating system level, not the server level. Regardless of what you call it, the second form of server virtualization implements a 1:M scheme, making one physical server appear to be many.

What you have is a very interesting situation. You have a technology that makes one server appear to be many (operating system virtualization) and another technology that makes many servers appear to be one (server virtualization). I'm sure you've guessed that this makes these two types of virtualization extremely complementary.

Basically, you can make all those virtual servers created via operating system virtualization appear to be one server using server virtualization. This makes it easier to scale up an application dynamically, because clients are talking to the virtual server on the application delivery controller and it talks to the virtual servers deployed on the physical servers inside the data center. The number of servers inside the data center can change without ever affecting the security, acceleration, and availability of the application because those functions are centralized on the application delivery controller and it can be automated to seamlessly add and remove the servers inside the data center.

There are more types of virtualization, at least six more, and they all fit into the big picture that is the next generation data center. For a great overview of eight of the most common categories of virtualization, check out this white paper.