How would someone edit terrain in gameplay?

I want a game where someone can manipulate the terrain in anyway during game play. Sorta like minecraft where you can manipulate terrain but not really in block form. Theres probably a simple answer to this, so sorry if this is a stupid question.

Unity terrain uses 2D heightmaps thus you can’t have caves, overhangs etc. You can only change the Y height of any given vertex in the terrain and I think that’s not what you are looking for. You need to either create or buy a voxel terrain system. Something like Voxelform.