View source for Oscilloscopes and waveform generators

An oscilloscope is a device that lets you analyze electrical signals. Its use is often indispensable when designing, debugging or simply using electronic circuits.

A signal generator is a device  capable of producing electrical signals (typically ''periodic'' signals), the characteristics of which can be specified by the user. The main characteristics of a periodic signal are waveform, amplitude, and frequency.

A good introductory guide to signals and oscilloscopes can be downloaded from http://www.tek.com/Measurement/App_Notes/XYZs/.