ASCII art is the art of manually creating graphics and images only out of fixed-width ASCII characters. This means no unicode or extended ASCII characters are allowed, of course. ASCII art is also, strictly speaking, separate from mere ASCII rendering, i.e. automatically rendering a bitmap image with ASCII characters in place of pixels, and ASCII graphics that utilizes the same techniques as ASCII art but can't really be called art (e.g. computer generated diagrams). Pure ASCII art should make no use of color.
This kind of art used to be a great part of the culture of earliest Internet communities for a number of reasons imposed largely by the limitations of old computers -- it could be created easily with a text editor and saved in pure text format, it didn't take much space to store or send over a network and it could be displayed on text-only displays and terminals. The principle itself predates computers, people were already making this kind of images with type writers. Nevertheless the art survives even to present day and lives on in the hacker culture, in Unix communities, on the Smol Internet etc. ASCII diagram may very well be embedded e.g. in a comment in a source code to explain some spatial concept -- that's pretty KISS. We, LRS, highly advocate use of ASCII art whenever it's good enough.
Here is a simple 16-shade ASCII palette (but watch out, whether it works will depend on your font):
#OVaxsflc/!;,.- . Another one can be e.g.:
_,,_ / ';_ . ( 0 _/ "-._ |\ \_ /_==-"""' | |:---' ( \ \__." ) Steamer '--_ __--' Duck! |L_        XX XX  XXXX        SAF FTW ^ | | _.--._ _.--._ | .' '. .' '. |/__________\____________/__________\______ | \ / \ | '. .' '. | `'--'` `'- | V
All content available under CC0 1.0 (public domain). Send comments and corrections to drummyfish at disroot dot org.