In the most general sense, think of analog as the opposite of digital. It came first, for example, music recorded on cassette tapes or computer documents saved on floppy disks are magnetic in nature and therefore analog.
In the technical sense, analog refers to electronic transmission accomplished by adding signals of varying frequency (or amplitude) to carrier waves of alternating electromagnetic current. Broadcast and phone transmission have conventionally used analog technology. Analog also connotes any fluctuating, evolving, or continually changing process. It is usually represented as a series of sine waves.
The term originated because the modulation of the carrier wave is analogous to the fluctuations of the voice itself. Another example is a modem, which is used to convert the digital information in your computer to analog signals for your phone line and vice versa, to convert analog phone signals to digital information for your computer.
On February 17, 2009, television sets based on technology used for the past 60 years will cease to
work. In 2006, Congress will decree that broadcasters must end analog transmissions on that date and switch to the digital technology they have been phasing in for several years. So if you're planning on buying a TV anytime soon, make sure it is digital-ready. Post digital? It's VoIP.