Default :

#VRML V2.0 utf8
#default cylinder

Shape{
geometry Cylinder{}
}

In addition to height and radius, Cylinder{} syntax has:

Cylinder{
radius 1
height 2
bottom TRUE
side TRUE
top TRUE
}

The Cylinder{} is the first primitive that uses parts. VRML considers a cylinder to consist of three parts: a top, bottom and side. The line:

tells the browser to render the "top" part of the Cylinder{}. The value for the field is TRUE. The value for a parts field must be a boolean. That is, either TRUE or FALSE (all capital letters). Try altering some of the fields:

#VRML V2.0 utf8

Shape{
geometry Cylinder{
height 3
radius .5
top FALSE
bottom FALSE

}

}