Backronym
A backronym, bacronym, or retronym is an acronym where the words represented by the individual letters are chosen after the fact to justify the shortened version. For instance, an environmental agency may want the acronym "GREEN" to represent their new information campaign, because the color green is associated with plants. To justify the desired acronym, they decide it will stand for "Great, Really Excellent Environmental News." In this example, the acronym was chosen before the words it represents, so it is a backronym.
The term "backronym" may also refer to an acronym perpetuated falsely in popular culture or folklore. For example, it is popularly believed that the distress signal "SOS" is an acronym for "Save Our Ship" or "Save Our Souls." In truth, the letters "SOS" were chosen solely because they are unmistakable when transmitted in Morse code.
Computer-related backronyms
A famous computer-related backronym is LISA (Local Integrated Software Architecture), the name of an early Apple computer. The acronym was chosen by Steve Jobs because his daughter's name is Lisa, and the words it represents were chosen later, arbitrarily.
The name of the Perl programming language is not an acronym, according to its creator, Larry Wall. However, he has enthusiastically endorsed two backronyms for Perl: "Practical Extraction and Report Language," and "Pathologically Eclectic Rubbish Lister."
BASIC is an acronym for Beginner's All purpose Symbolic Instruction Code, and is not a backronym.