As much as I hate to disagree with professional colleagues, I'm afraid I have to in this case; much of what's been given in earlier responses is, unfortunately, incorrect. It comes from some very common misconceptions and confusion of terms, but it's very definitely wrong.

By definition, an “analog” signal is simply one in which some parameter of the signal varies analogously (i.e., “in a manner similar”) to the information being conveyed. In an electrical signal, very commonly what’s varied is the voltage or amplitude, as in the case of the output of a microphone; the amplitude of that signal varies in the same way as the sound pressure which was “heard” by that microphone. More generally, “analog” (as is also the case with the term “digital”) refers to a means of encoding information on to a signal, and that is all it means.

“Analog” is not a synonym for “continuous,” “linear,” etc., nor do analog signals somehow possess “infinite resolution” or any other such nonsense. (And similarly, “digital” is not a synonym for “discrete,” “sampled,” “quantized,” etc. - it simply means a system in which information is conveyed as numeric values, or “digits.”) You can have sampled analog systems, and in a given situation a digital representation may provide a good deal greater resolution/accuracy than any possible analog option. Also note that from this perspective, there is no such thing as “digital” or “analog” electronics; all electronic circuits operate under the same set of basic principles, although they may clearly be optimized for dealing with information in either digital or analog form.

And finally, the world itself - the reality in which we live - is neither “digital” nor “analog.” Reality is simply reality; it’s the original information, and these two terms again refer solely to means of encoding that information for transmission, processing, or storage. There are more than these two options, too; everything doesn’t somehow neatly fit into one of these two buckets. Power electronics, for instance, are neither digital nor analog (although parts of their control paths may be), as the output of a power supply does not provide information content. Yes, it may be “continuous,” etc., but those are all perfectly good descriptive terms already available for our use - we don’t need to senselessly co-opt the terms “digital” and “analog” to serve as poor stand-ins for them.