Interactive Fiction: Gameplay is language-based in nature. All interaction with the player, both input and feedback, is done through the input and output of pure text. Input mimics natural language using verb-noun (action-item) commands (Abbreviations also qualify, because they abbreviate a verb-noun construct, like "w" for "go west" or "i" for "list inventory"). Output is rendered in full, natural-language, grammatically-correct sentences.
Sometimes referred to as "text-adventure" or "Infocom" games (after the company that made them famous). Part of the Non-Sports Themes category.
You can browse through games in the MobyGames database that are part of this genre via the game browser.