A hand-held slide viewer is a portable device that enables the magnified viewing of microscopic slides. It consists of a magnification lens, light source, slide holder, focus adjustment knob, and eyepiece. Applications include education, medicine, and science, where high-magnification slides need to be viewed for magnified observation and analysis. Common types include basic viewers for casual use, advanced viewers with adjustable features, and specialized viewers for professional applications. Accessories like carrying cases, slide trays, cleaning kits, and calibration slides enhance usability.