BASIC was available for almost any system of the era and became the de facto programming language for home computer systems that emerged in the late 1970s. These PCs almost always had a BASIC interpreter installed by default, often in the machine's firmware or sometimes on a ROM cartridge.
In general, basic or basics describes anything covering all the necessary facts or essentials required for a subject or skill. For example, anyone with a basic understanding of computers has a general understanding of how to use and operate a computer.