Blue-book D&D

Blue-book D&D, p.n. 1. the 1974 edition of TSR Hobbies, Inc.'s Dungeons & Dragons Adult Fantasy Role-Playing Game. 
2. D&D as played by this basic rules set. 
3. a D&D game with characters below 3rd level (the bluebook rules only covered characters through third level - more advanced players moved on to the AD&D rules). 
4. any D&D game played with simplified rules. [GJ1]
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Addendum: So-called because the rules were published in a single soft-cover volume with a blue cover. This volume was included, along with an introductory module and a set of polyhedral dice (later chits), in a boxed "Basic Set" with a color cover illustration. A final 3rd Edition was published in 1979. [GJ1]
Addendum #2: Many later "dungeon crawl"-based computer games, such as NetHack, used a rules system derivative of, or directly stolen from, the D&D bluebook rules. [GJ1]