What do the category codes like SM, EZ, MU mean?

SM is State Merit, the open merit list everyone competes in. The reservation codes are: EZ (Ezhava), MU (Muslim), BH (Other Backward Hindu), LA (Latin Catholic and Anglo-Indian), DV (Dheevara and related), VK (Viswakarma and related), KN (Kudumbi), BX (Other Backward Christian), and KU (Kusavan and related). SC is Scheduled Caste, ST is Scheduled Tribe, and EW is Economically Weaker Section. Your certificate determines which single reservation column applies to you, and everyone is considered under SM first.