Source : Webster's Revised Unabridged Dictionary (1913)

Scoria \Sco"ri*a\, n.; pl. {Scori[ae]}. [L., fr. Gr. ?, fr. ?
   dung, ordure.]
   1. The recrement of metals in fusion, or the slag rejected
      after the reduction of metallic ores; dross.

   2. Cellular slaggy lava; volcanic cinders.

Source : WordNet®

scoria
     n : the scum formed by oxidation at the surface of molten metals
         [syn: {slag}, {dross}]
     [also: {scoriae} (pl)]