C64 BASIC was unusual for the time as it allowed you to create and manipulate text string variables without having to reserve space or define them before using them.
This ease of use of BASIC and immediate understanding of how strings worked meant that many of us 1980s kids could easily create text-heavy “choose-your-own adventure” style games.
These are games where instead of moving a joystick to control a character on screen, the player could make decisions that changed the outcome of a story, such as "Do you climb the ladder? Yes/No".
Having a fixed choice of optional directions or decisions meant the style of game is sometimes described as a “story with options” rather than an “adventure” per se, but even the books in print often offered random elements and even player character development using upgrades and health stats.
Sometimes these style of adventures are called Game Books (or Gamebooks). I quite like that, and prefer it over the stuffy-sounding Interactive Narrative Adventure. As a general term, apparently the correct phrase to use is “Interactive fiction“, but that covers a huge range of ideas.