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Popular when home computers had only minor (if any) graphics capability.
User interaction in these games consisted of typing commands like "HELP", "SOUTH", "OPEN DOOR", and "PUT BABELFISH IN EAR".
Most well-known company producing these games was Infocom, who produced the "Zork" series and many other titles still fondly remembered by countless fans.
First title (or at least best known to be first) was available on Unix(?) mainframes, called the "Cave Adventure" (or more commonly "The Original Adventure").
Also known as interactive fiction.