This document discusses different types of defects in solids. It begins by classifying defects as either point defects, involving irregularities around a single atom, or line defects, involving irregularities in rows of atoms. Point defects are further broken down into stoichiometric defects (e.g. vacancies, interstitials), impurity defects, and non-stoichiometric defects. Specific stoichiometric point defects discussed include vacancy defects, interstitial defects, Schottky defects, and Frenkel defects. The document also discusses impurity defects caused by substitutional or interstitial impurities.