When an opera is played without staging (be it either a rehearsal or an actual concert) it is called all'italiana (translated: "in the italian style"). Or, at least, this is how we call it here in Italy.
This term is used when the singers are not wearing any scene dress, they just stand up near the director and the orchestra is on stage (not in the pit).
Why is it called like this? Is there any particular historical reference to italian opera? I don't recall any work of Verdi, Rossini or Puccini being written to be played without staging. So where is this term coming from?