This document discusses different types of conicoids and their properties. It defines a conicoid as a surface whose cross sections are conic sections. There are four types of central conicoids based on the signs of coefficients in their equation: ellipsoid, hyperboloid of one sheet, hyperboloid of two sheets, and virtual quadric. Properties discussed include plane sections, tangency, enveloping cones/cylinders, polar planes, and paraboloids. Conjugate points, lines, and diametral planes are also defined. The document provides mathematical conditions and definitions for many geometric properties and concepts relating to conicoids.