Used prenominally to describe something done or expressed openly, officially, or in a public manner, as opposed to privately or behind the scenes. Often contrasts with 内々 (privately).
From 表 (おもて, 'front, surface, public') + 立つ (たつ, 'to stand') in its past/perfective form 立った, literally 'having stood on the surface', used prenominally to mean 'public, open'.
