'ATASCII' means 'Atari ASCII.' It was a character set specific to Atari's 8-bit line of computers.
The ATASCII character set contained English alphanumeric characters, plus other shapes and symbols. People would arrange these symbols on the screen to make illustrations and art.
It was also possible to create rudimentary animations by using terminal commands to move the cursor around the screen. These animations could then be saved as text files and played back later.
Here are a few places to learn more about ATASCII and ATASCII animations:
See some of Break Into Chat's other special collections.
Interested in BBSing, door games, or retrocomputing? Check out the Break Into Chat BBS wiki or the blog.