VRML (Virtual Reality Markup Language) is a standard descriptive language for 3-dimensional objects. Many web browsers can view VRML files directly or will automatically attempt to download so-called "plugin" software that enables viewing of virtual reality models.
Alternatively one can download what is known as a "helper" application (which runs independently of your browser) and configure your browser to start this helper when a link to a VRML file is selected.
There is some help available from NIST (National Institute of Standards and Technology).
You might also want to have a look at George Hart's page that describes the process of installing and configuring a VRML viewer.