"BECMI" refers to the Frank Mentzer 1983 edition of Basic, Expert, Companion, Masters, and Immortals Dungeons & Dragons. This edition might also be considered to cover the Allston-era Rules Cyclopedia, though the latter altered many of Frank's rules.
This is the successor to the Moldvay/Cook/Marsh "BX" D&D game.
Use this tag to indicate interest specifically in the BECMI version of D&D. Use Classic D&D to indicate broader interest in any version of original or basic D&D, including BECMI. Use Basic D&D to indicate interest in any version of Classic D&D other than OD&D. You might also want to use D&D Rules Cyclopedia, since many fans consider the Rules Cyclopedia and BECMI rules to be equivalent.