noun-modifying (irregular)
public; open; formal; official
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).
表立った批判は避けたほうがいい。
It's better to avoid open criticism.
彼は表立った活動には参加しなかった。
He didn't take part in any public activities.
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'.