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.

(n.) A method of computing solid volume data for graphical display in volumetric models that are composed of 3-D elements which are called voxels. Direct volume-rendering techniques enable you to manipulate the volume data as a solid structure that you can slice to expose internal views.

Volume rendering is a technique used to display a 2D projection of a 3D discretely sampled data set.