This document discusses x-rays and their production and properties. It describes how x-rays are generated using a Coolidge tube by accelerating electrons into a metal target. This produces both a spectrum of x-ray wavelengths via bremsstrahlung and characteristic x-ray lines. Units used to measure x-ray properties like intensity and absorption are defined. The document also discusses how x-ray absorption depends on the electron density and thickness of absorbers, allowing their use in medical diagnosis.