Volume rendering is a direct technique for visualizing volume primitives without any intermediate conversion of the volumetric dataset to surface representation. [KAU91
Computer visualization of 3D images from arbitrary angles without explicit definition of surface geometry.
(n) A visualization technique used with three independent variables mapped to the three geometric dimensions. Each dependent data value is represented by a 3-D volume unit called a voxel, typically coded with color. Various sectioning techniques are used to reveal data values on the interior of the data space.